CN110995299B - Electromagnetic wave orbital angular momentum transmission method and system based on dimension expansion interference code - Google Patents

Electromagnetic wave orbital angular momentum transmission method and system based on dimension expansion interference code Download PDF

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CN110995299B
CN110995299B CN201911059639.6A CN201911059639A CN110995299B CN 110995299 B CN110995299 B CN 110995299B CN 201911059639 A CN201911059639 A CN 201911059639A CN 110995299 B CN110995299 B CN 110995299B
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张超
蒋金
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Tsinghua University
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/06—Receivers
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
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    • H04B7/0408—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas using two or more beams, i.e. beam diversity

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Abstract

The invention relates to an electromagnetic wave orbital angular momentum transmission method and system based on dimension expansion interference codes. In the system, the signal transmitting terminal system comprises a data generating module, a serial-parallel conversion module, an interference code dimension expanding module, an OAM mode selecting module and a signal transmitting antenna module. The data generation module outputs modulated serial user data; the serial-parallel conversion module converts serial user data into a plurality of lines of parallel data; the interference code dimension expansion module multiplies the parallel data with an interference code to form a dimension expansion matrix; the mode selection module adds elements of each column vector of the dimension expansion matrix respectively and feeds the elements to the antenna array through different modes to be converted into space electromagnetic waves to be emitted. At the receiving end, the signal receiving end subsystem comprises a receiving antenna array and a data demodulation module, and the receiving antenna array sends the received spatial transmission electromagnetic waves to the demodulation module. The demodulation module recovers the transmitted signal as user data. The invention improves the signal-to-noise ratio of the receiving end, reduces the resolving complexity of the receiving end and can be applied to multi-user transmission.

Description

Electromagnetic wave orbital angular momentum transmission method and system based on dimension expansion interference code
Technical Field
The invention belongs to the technical field of orbital angular momentum electromagnetic wave communication, and particularly relates to an electromagnetic wave orbital angular momentum transmission method and system based on dimension expansion interference codes.
Background
The Orbital Angular Momentum (OAM) of an electromagnetic wave is another important physical quantity distinguished from the electric field strength of an electromagnetic wave. The electromagnetic wave with OAM is also called "vortex electromagnetic wave", and its phase plane appears spiral along the propagation direction, which is not a conventional planar electromagnetic wave. The electromagnetic waves of different OAMs can be orthogonally transmitted at the same frequency, and a new dimension is opened for the multiplexing of the electromagnetic waves. The method is expected to be applied to communication, navigation and radar, can greatly improve the communication transmission capacity and the navigation precision and the radar detection precision, and is an important direction for future development of electromagnetic wave application.
Research on electromagnetic wave Orbital Angular Momentum (OAM) has been in history for over thirty years, and primarily focuses on the optical communication field, and has not been gradually extended to the low-frequency electromagnetic wave field, i.e., microwave, millimeter wave and terahertz wave band until the last decade, and a communication system with electromagnetic wave OAM can greatly improve the transmission capacity of the system by virtue of OAM orthogonality. The orthogonality of OAM modes brings additional spectral and energy efficiency, which is first realized and applied in optical communications. Because the OAM modes in the optical fiber are mutually orthogonal due to the orthogonality among different orders of OAM, the OAM modes overlapped in a plurality of spaces can be demodulated into a Gaussian mode by using a reverse phase plate, so that the OAM modes are mutually separated in space, a complex DSP algorithm is omitted in a demodulation system, and the complexity of the system is greatly reduced. OAM mode multiplexing may be used to increase the number of channels and increase communication capacity. Circularly polarized light with spin OAM was first predicted by Poynting in 1909. The mechanical effect of circularly polarized light was observed for the first time in 1936 experiments. Since then, the research on electromagnetic wave OAM in the scientific community has almost stopped. Until 1992, Allen did not suggest that the laguerre gaussian laser beam has OAM and could be used as an optical wrench or to increase the transmission channel capacity. In 2012, Jian Wang et al achieved a transmission rate of 1.37Tbps using the orbital angular momentum properties of the laser. In 2013, Nenad B. et al utilize two OAM mode multiplexing and polarization state multiplexing to realize a transmission distance of 1.1km and a transmission rate of 400Gbit/s, and combine wavelength division multiplexing of ten wavelengths to realize a transmission rate of 1.6Tbit/s, and a communication system does not use DSP algorithm for demodulation, thereby simplifying the complexity of a receiver. A Jinxianxian team of Shanghai university of transportation develops an optical waveguide capable of carrying photon OAM freedom degree in a first optical chip in 12 months in 2018, and realizes efficient and high-fidelity transmission of photon OAM in the waveguide.
Compared with optical communication, radio frequency electromagnetic waves (below 300 GHz) are difficult to generate and apply orbital angular momentum quantum states, and long-distance transmission of radio frequency OAM beams in free space is difficult due to beam divergence. B.tide et al first popularized OAM in the optical domain to the microwave band in 2007, and proposed that a Uniform Circular Array (UCA) antenna could generate microwave orbital angular momentum, and thought that microwave OAM would also improve the transmission rate of radio frequency information, and alleviate the problem that the frequency band is largely occupied. Since uniform circular antenna arrays can easily generate orbital angular momentum carrying different modes, much of the research hereafter is also based on uniform circular antenna array schemes. In 2010, Mohammadi analyzed in detail the generation and detection of different OAM electromagnetic waves with a uniform circular antenna array. The receiving end adopts a receiving antenna with an opposite OAM mode to the transmitting end to receive the energy of the whole annular wave beam from the space, the transmitted OAM electromagnetic wave is changed into a conventional plane electromagnetic wave after being subjected to phase compensation by the receiving antenna, and the conventional electromagnetic wave after the phase compensation can be separated out in a space division mode because the radius of the annular wave beam of the OAM electromagnetic waves with different modes is increased along with the positive proportion of the mode number. This full spatial domain reception method is referred to from optical OAM. In 2014, Yan Yan et al utilized a full-airspace receiving method to multiplex four OAM modes at a distance of 2.5m, the transmission rate was 32Gbit/s, and the spectrum efficiency reached 16 bit/s/Hz. The existing electromagnetic wave OAM full-phase-plane coaxial transmission mode is analyzed, and the following results can be found: with the increase of the number of the OAM modes, the OAM electromagnetic wave divergence angle is increased, the electromagnetic wave beam emitted from the transmitting antenna is in an inverted cone shape, and the longer the transmission distance is, the more the beam is diverged. If the method for coaxially receiving the full phase plane in the optical fiber is adopted, a huge annular receiving antenna coaxial with the propagation direction is needed, and the method cannot be realized in a practical environment. Therefore, the receiving method in the full space domain is only suitable for short-distance point-to-point transmission. Because the phases of the OAM electromagnetic waves are linearly distributed along the circumference on the ring-shaped beam cross section, there is a phase difference between any two points on the ring-shaped beam cross section, and the phase differences generated by the electromagnetic waves of different OAM modes are different. When the antenna spacing is fixed, the phase difference between the antennas is in direct proportion to the OAM mode. Therefore, antenna array receiving signals can be arranged on part of the annular wave beams, detection of different phase differences can be completed by performing Fourier transform on the receiving signals, and detection and separation of different OAM modes can be further completed. In 2016, experiments of 10m and 160Mbit/s transmission rate were carried out by people group in Zhejiang university chapter and other subjects using partially received 4 paths of OAM electromagnetic waves. However, the phase gradient detection requires that the two receiving points are both located on the same circumference perpendicular to the propagation axis, and the center of the circle coincides with the propagation axis. Phase misalignment will reduce the accuracy of OAM modal detection. Moreover, the detection accuracy decreases with decreasing opening angle between the two antennas, namely: when the antenna pitch is fixed, the detection accuracy decreases as the transmission distance increases, and further, the detection performance thereof is greatly affected by noise. In 2016, an avionics laboratory of Qinghua university receives OAM electromagnetic waves by using a part of phase surfaces, and the OAM is mapped to a second frequency domain by rotating the OAM electromagnetic waves, so that a transmission experiment of 10GHz OAM electromagnetic waves with a long distance of 27.5 kilometers (from Qinghua university to Qianling mountain) is completed; and in 2018, in 4 months, a 172 km (Boa mountain to Bo-ren) airborne OAM multiplexing transmission experiment is successfully carried out.
The orbital angular momentum transmission scheme using UCA antennas is considered to be an efficient line-of-sight MIMO scheme with high spectral efficiency. However, multi-antenna joint demodulation requires processing of multi-antenna signals, resulting in high complexity of receiver solution. In order to overcome the inter-modal interference, 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 prominent in the case of non-co-axial between transmit (Tx) and receive (Rx) array antennas. Therefore, the invention innovatively provides an electromagnetic wave orbital angular momentum transmission method and system based on the dimension-expanding interference code, and the interference code is adopted to expand on different modes of multiplex transmission. Due to the orthogonality of the interference codes, the finally transmitted OAM wave beams form space division wave beams through self-interference, energy of each wave beam is concentrated in the direction of a corresponding receiving antenna, and can be easily received by corresponding antennas in UCA, so that the signal-to-noise ratio (SNR) of a receiving end is improved, and the structure of a receiver is simplified. In addition, the scheme does not need to consider inter-modal interference, and the space division beams can be distributed to a plurality of users to form a multi-user OAM transmission scheme.
Disclosure of Invention
The invention aims to solve the problem of high resolving complexity of multi-antenna joint demodulation in the UCA antenna scheme and the problem of interference between OAM modes under the condition that a transmitting end and a receiving end are not coaxial to a certain extent.
Therefore, the invention aims to provide an electromagnetic wave orbital angular momentum transmission method and system based on the dimension-expanding interference code, the system simplifies the receiver structure in the UCA antenna scheme of OAM, improves the signal-to-noise ratio of a receiving end, realizes multi-user transmission, and greatly inhibits the problem of interference between modes under the condition that the receiving end and the transmitting end are not coaxial.
The utility model provides an electromagnetic wave orbit angular momentum transmission system based on dimension expansion interference code, includes signal transmission terminal system and signal receiving terminal subsystem, wherein:
the signal transmitting terminal system comprises a data generating module, a data serial-parallel conversion module, an interference code dimension expanding module, an OAM mode selecting module and a signal transmitting antenna module which are connected in sequence,
a data generating module for receiving user data and outputting modulated serial user data;
the data serial-parallel conversion module is used for converting the serial user data into a plurality of lines of parallel data according to the OAM mode number;
the interference code dimension expanding module is used for multiplying the parallel data by an interference code, carrying out dimension expanding operation on the parallel data and changing the parallel data into a dimension expanding matrix with the same dimension as the OAM modal number, wherein the interference code is a sequence with orthogonality or quasi-orthogonality;
the OAM mode selection module is used for respectively adding elements of each column vector of the dimension expansion matrix and selecting different OAM modes to feed to uniform circular array antenna arrays of different OAM modes of the signal transmitting antenna module to form different OAM mode carrier signals;
a signal transmitting antenna module for converting different OAM mode carrier signals into space electromagnetic waves and transmitting the space electromagnetic waves,
the signal receiving end subsystem comprises a receiving antenna array and a data demodulation module, wherein the receiving antenna array is positioned on the same annular cross section where different OAM mode wave beams converge, each wave beam corresponds to one receiving antenna, each receiving antenna converts received space electromagnetic waves into radio frequency signals respectively and sends the radio frequency signals to the data demodulation module, and the data demodulation module recovers the radio frequency signals into user data of each path.
An electromagnetic wave orbital angular momentum transmission method based on dimension-expanding interference codes adopts the transmission system to carry out the following steps:
the data generation module receives the user data and outputs modulated serial user data;
the data serial-parallel conversion module converts the serial user data into a plurality of lines of parallel data according to the number of the OAM modes;
the interference code dimension expanding module multiplies the parallel data by interference codes, performs dimension expanding operation on the parallel data to become a dimension expanding matrix with the same dimension as the OAM modal number, and the interference codes are sequences with orthogonality or quasi-orthogonality;
the OAM mode selection module adds elements of each column vector of the dimension expansion matrix respectively and selects different OAM modes to feed to the antenna arrays of the uniform circular arrays of different OAM modes of the signal transmitting antenna module to form different OAM mode carrier signals;
the signal transmitting antenna module converts different OAM mode carrier signals into space electromagnetic waves and sends the space electromagnetic waves out;
the receiving antenna array is positioned on the same annular cross section where different OAM mode wave beams converge, each wave beam corresponds to one receiving antenna, each receiving antenna converts received space transmission electromagnetic waves into radio frequency signals and sends the radio frequency signals to the data demodulation module, and the data demodulation module recovers the radio frequency signals into user data.
The present invention aims to solve the problems of low received signal-to-noise ratio due to beam divergence and high receiver complexity of the MIMO scheme in the free space electromagnetic wave orbital angular momentum transmission described in the background, and inter-modal interference and single-user-only reception therein. Therefore, the invention aims to provide an electromagnetic wave orbital angular momentum transmission method and system based on the dimension-expanding interference code, and the method can improve the signal-to-noise ratio of the electromagnetic wave orbital angular momentum transmission receiving end and reduce the resolving complexity of a receiver. In addition, the scheme inhibits the interference between the OAM modes of the UCA and solves the problem that the UCA can only be used for single-user receiving. The scheme proposed by the present patent can be applied to multi-user transmission, which will be described in detail in the following examples.
Drawings
The above features and technical advantages of the present invention will become more apparent and readily appreciated from the following description of the embodiments thereof taken in conjunction with the accompanying drawings.
FIG. 1 is a schematic structural diagram of an electromagnetic wave orbital angular momentum transmission system based on a dimension-expanding interference code according to the present invention;
fig. 2-1 is a schematic diagram of a planar coaxial UCA model;
fig. 2-2 is a schematic diagram of a circular longitudinal coaxial UCA model;
FIG. 3 is a schematic diagram of a multiple longitudinal uniform circular antenna array coaxial transmitting and receiving configuration of the present invention;
fig. 4 is a spatial energy distribution diagram of a single shaped beam in OAM multiplexing transmission according to an embodiment of the present invention;
FIG. 5 is a circular cross-sectional view of a multiplexed beam directed energy distribution of an embodiment of the present invention;
FIG. 6-1 is a graph illustrating a received energy distribution of users in neighboring locations with beam pointing locations, in accordance with an embodiment of the present invention;
FIG. 6-2 is a diagram illustrating a distribution of the received energy of the users at diagonal positions of the beam pointing positions according to an embodiment of the present invention;
fig. 7 is a diagram illustrating multi-user transmission according to an embodiment of the present invention.
Detailed Description
The following describes embodiments of the electromagnetic wave orbital angular momentum transmission method and system based on the dimension-spreading interference code according to the present invention with reference to the accompanying drawings. Those of ordinary skill in the art will recognize that the described embodiments can be modified in various different ways, or combinations thereof, without departing from the spirit and scope of the present invention. Accordingly, the drawings and description are illustrative in nature and not intended to limit the scope of the claims. Furthermore, in the present description, the drawings are not to scale and like reference numerals refer to like parts.
As shown in fig. 1, 2-1 and 2-2, the electromagnetic wave orbital angular momentum transmission system based on the extended dimension interference code comprises a signal transmitting terminal system and a signal receiving terminal system. The signal transmitting terminal system comprises a data generating module 101, a data serial-parallel conversion module 102, an interference code dimension expanding module 103, an OAM mode selecting module 104 and a signal transmitting antenna module 105, wherein the signal transmitting antenna module 105 comprises a planar coaxial UCA mode 109 and a circular longitudinal coaxial UCA mode 110; the signal receiving end subsystem includes a receiving antenna array 106, a data demodulation module 107 and a user receiving end module 108. The following describes the structure of each subsystem.
1. Signal transmitting subsystem
(1) The data generation module 101: generates user data and outputs the modulated serial user data. The modulation method may be Amplitude Shift Keying (ASK), Frequency Shift Keying (FSK), Phase Shift Keying (PSK), or Quadrature Amplitude Modulation (QAM), Minimum Shift Keying (MSK), Orthogonal Frequency Division Multiplexing (OFDM), or the like.
(2) The data serial-parallel conversion module 102: converting serial user data into multi-line parallel data according to the number of the OAM modes;
(3) interference code dimension expanding module 103: multiplying the parallel data by an interference code, performing dimension expansion operation on the parallel data to form a dimension expansion matrix with the same dimension as the OAM mode number, wherein the interference code is a sequence with certain orthogonality or quasi-orthogonality, due to the orthogonality of the interference code, the finally transmitted OAM wave beam forms space division wave beams through self-interference, and the energy of each wave beam is concentrated in the direction of a corresponding receiving antenna and can be easily received by a corresponding antenna in the UCA of a receiving end.
The interference code is a sequence set having a certain orthogonality. Without loss of generality, the dimension extending process is described below by taking a carrier interference code (CI code) as an example. The process of constructing the CI code from the vector quantities of the fourier transform matrix is:
FN＝[Wi,k]N×N (2)
wherein the content of the first and second substances,
Figure GDA0002732830580000051
when N is 2n,n∈Z+In the case of (A), FNIs a DFT (discrete Fourier transform) matrix, and the row vectors of the DFT matrix are orthogonal two by two. The CI code includes interference code 1 through interference code N-1, which can be expressed as
C＝[c0,c1,…,cN-1]T (3)
Wherein, ci＝[Wi,0,Wi,1,…,Wi,N-1]I is more than or equal to 0 and less than or equal to N-1. As shown in fig. 1, it is assumed that user data is converted into parallel data D ═ D after serial-to-parallel conversion0,d1,…,dN-1]TI.e. in FIG. 1The symbols 1 to N-1 are subjected to interference code dimension expansion module, and the sent CI-OAM signal (dimension expansion signal matrix) S is a Hadamard product of D and C
Figure GDA0002732830580000061
Wherein the content of the first and second substances,
Figure GDA0002732830580000063
expressing a Hadamard product, C expressing a CI code dimension expansion matrix, sending each row of the S matrix in one OAM mode, and then sending a signal on the OAM mode l by the k row dimension expansion signal matrix
Figure GDA0002732830580000062
(4) OAM modality selection module 104: parallel data transmitted by the same OAM mode are overlapped, namely, column vector addition is carried out on an input dimension expansion matrix, a corresponding OAM mode is selected and fed to UCA antenna arrays of different OAM modes to form different OAM mode carrier signals, namely, the addition of elements in the first column of S is sent by an OAM mode 0, the addition of elements in the second column is sent by an OAM mode 1, and the like, and the addition of the elements in the Nth column is sent by an OAM mode N-1.
In the above, only a plurality of rows of parallel data are formed, the parallel data are expanded into an expanded dimension matrix, and the columns of the expanded dimension matrix are orthogonal. Or forming a plurality of columns of parallel data, expanding the parallel data into an expanded dimension matrix, and then enabling the rows of the expanded dimension matrix to be orthogonal. The principle and method are the same and are not described in detail herein.
(5) The signal transmitting antenna module 105: for converting different OAM modal carrier signals into spatial electromagnetic waves, it includes either one of two modes of a planar coaxial UCA mode 109 and a longitudinal coaxial UCA mode 110.
As shown in fig. 2-1, the planar coaxial UCA module 109 includes a plurality of coaxial (i.e., surrounding the same propagation axis) uniform circular antenna arrays in the same plane, where the same circle of arrays are completely the same, the amplitudes of the feed signals are equal, the phases are uniformly delayed once, and the total phase delay is l · 2 pi when the feed signals rotate around the propagation axis, where l is the OAM modal number. 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 accurately calculated, so that different OAM mode beams are finally converged on the same annular section, and the radius of each UCA can be calculated according to the same beam divergence angle and electromagnetic wave frequency of different coaxial OAM modes in the same plane through a formula 6.
Figure GDA0002732830580000071
Formula 6 is an electric field expression of UCA-based OAM in a spherical coordinate system (r, θ, Φ), where OAM airspace electric field intensity E, r represents a linear distance from the center of the circular array to an observation point, l is an OAM modal number, N represents the number of antenna elements in UCA, J isl(. is a Bessel function of order I,
Figure GDA0002732830580000072
is the wave vector, lambda is the electromagnetic wave wavelength,
Figure GDA0002732830580000073
a is the radius of the UCA antenna array at the transmitting end, and theta is the OAM wave beam divergence angle. For example, knowing the same beam divergence angle, electromagnetic wave frequency, and the same annular cross section to be converged at last, the UCA radius of each transmitting end can be calculated according to formula 6, and the position of the transmitting end can be located according to the same annular cross section to be converged at last.
As shown in fig. 2-2, the vertical coaxial UCA module 110 is composed of a plurality of identical vertical uniform circular antenna arrays, each uniform circular antenna array generates different OAM modes, and since each OAM mode is different and the beam divergence angle is different, the antenna placement position needs to be accurate. Firstly, beam divergence angles of different OAM modes are calculated according to electromagnetic wave frequency and the radius of the uniform circular antenna array, the electromagnetic wave divergence angles can be obtained according to a formula 6, and in order to enable beams of different OAM modes to be finally converged on the same annular section, the positions of the annular antenna arrays can be determined through a geometric relationship according to the beam divergence angles corresponding to the annular antenna arrays and the positions of the same annular section to be converged;
the signal transmitting antenna module 105 may generate a spiral phase plane by a spiral phase plate, a spiral reflecting plane, or a circular phased array to obtain an electromagnetic wave signal with orbital angular momentum. The signal transmitting antenna module 105 may coaxially generate a plurality of modal OAM electromagnetic waves, the OAM electromagnetic waves of different modalities are orthogonal to each other during spatial transmission, the energy of the signal is mainly concentrated in a ring formed by the main lobe, and the OAM phase planes of the plurality of modal orthogonality are also uniformly distributed on the ring, so that different OAM modal beams are finally converged onto the same ring section of the receiving end.
2. Signal receiving subsystem
(1) The receive antenna array 106: the receiving antenna array is positioned on the same annular cross section converged by different OAM mode beams, and is used for converting space transmission electromagnetic waves (electromagnetic waves transmitted in free space) into radio frequency signals (namely guided electromagnetic waves in a transmission line) and sending the radio frequency signals to the data demodulation module, wherein 1 to N-1 antennas are arranged on the same annular cross section corresponding to the previous mode signals from 1 to N-1, and each mode beam corresponds to a different receiving antenna;
(2) the data demodulation module 107: demodulating the received radio frequency signal to recover user data;
(3) the user receiving end module 108: and sending the demodulation module data to a user receiving end.
The following describes the implementation principle of signal reception. The transmitting end can adopt any one of a longitudinal coaxial UCA mode 110 or a planar coaxial UCA module 109, and UCA antenna arrays containing M antennas are coaxially arranged at the receiving end, and the M antennas are uniformly distributed on a phase plane. For mode i, the phase difference between adjacent antennas is c. Without loss of generality, if antenna No. 0 is exactly in the initial phase direction of the transmission signal of all modes (here, the example of antenna No. 0 is only for convenience of description, and in fact, antenna No. 0 may be another number, in short, the initial phase direction of the transmission signal of one antenna in all modes), the phase factor matrix corresponding to the receiving antenna array may be represented as:
Figure GDA0002732830580000081
wherein, the phase factor of the l-th modal signal corresponding to the m-th antenna is
Figure GDA0002732830580000082
When M is equal to N, the compound is,
Figure GDA0002732830580000083
it can be easily seen that when the number of receiving antennas is less than that of transmitting antennas, i.e. M is less than N, the number of unknown receiving quantities is less than that of transmitting data, and the equation is an underdetermined equation and has no solution. When the number of the receiving antennas is more than that of the transmitting antennas, namely M is more than N, the number of the receiving unknowns is more than that of the transmitting data, an over-determined equation is obtained, and the least square solution of the receiving unknowns can be solved. To simplify the calculation and discussion, only the signals received at each receive antenna when M is equal to N are considered below. According to equation (5), the signal received by the receiving antenna No. 0 is:
Figure GDA0002732830580000084
the ith antenna receives signals as follows:
Figure GDA0002732830580000085
wherein the content of the first and second substances,
Figure GDA0002732830580000086
is additive white gaussian noise for the ith receiver, 0 is the noise mean,
Figure GDA0002732830580000087
is the noise variance. Therefore, only the corresponding data d is left on each receiving antenna of the i-th antennaiWith other data signals followingThe orthogonality of the rows and columns of the phase factor matrix cancels out each other. From the overall system perspective, data diAs if sent along a separate channel to the receive antenna riThe method and the device reflect the functions of the dimension-extending code in beam forming and beam regulation.
If the No. 0 antenna is not aligned in the initial phase direction of all the mode transmitting signals, the offset angle is set as phi, and
Figure GDA0002732830580000088
the signal received by the receiving antenna array at time t can be expressed as:
Figure GDA0002732830580000089
wherein r isi (φ)(t) represents a signal received from the i-th receiving antenna. Let formula (8) and formula (9) above denote that the received vector when Φ is 0 is r (t) ═ r0(t),r1(t),…,rN-1(t)]Then the correlation matrix of the received vector is:
R＝E[r(t)rH(t)] (11)
wherein the i-th of the matrix R1Line, i-th2The elements of the column are
Figure GDA0002732830580000091
Matrix piRepresents the cross-correlation matrix between the ith antenna signal after the offset angle phi and the received signal vector r (t):
Figure GDA0002732830580000092
according to the minimum mean square error criterion, the optimal weighting coefficient vector can be obtained as follows:
w(φ,t)＝R-1pi (13)
thus obtaining the output signal after the receiving antenna deflects phi as follows:
Figure GDA0002732830580000093
aligned for example with all modal primaries (i.e. start phases): parallel data is transmitted by a longitudinal coaxial UCA mode 110 comprising a plurality of identical circular antenna arrays, as shown in fig. 3, with four identical UCAs placed at different positions along the axis, each UCA producing a modal OAM. In the vertical axis direction, each UCA generates OAM modes l ═ 1, l ═ 2, l ═ 3, and l ═ 4, and its corresponding beam divergence angle is θ1＝11.26°,θ2＝18.91°,θ3＝26.47°,θ434.35. The spacing between transmitting UCAs and receiving UCAs is d1、d2、d3And d4. According to the system configuration shown in FIG. 3, the positional relationship can be calculated as
Figure GDA0002732830580000094
The annular radius R of the receiving antenna is 1m, and the position for solving each UCA is d1＝2.1m、d2＝0.91m、d30.55m and d4＝1.46m。
As shown in fig. 4, it can be seen that a single shaped beam far-field pattern multiplexed (at a receiving end, beams of each mode are accumulated at an initial phase aligned with 0 phase) when the number of the simulation OAM modes is l 1, l 2, l 3, and l 4, and each shaped beam points to a specific direction, and then a receiving antenna is placed in the direction, so that a maximum signal-to-noise ratio of far-field reception can be obtained. Fig. 5 shows the far-field pattern multiplexed by four antennas transmitting four OAM modes l 1, l 2, l 3, and l 4, and it can be seen that in the four phase directions of the torus
Figure GDA0002732830580000101
And
Figure GDA0002732830580000102
only the data transmitted by the corresponding antenna array is left by multiplying each receiving antenna by the corresponding phase factorOAM beamforming is now directed to different locations. And a receiving antenna is placed at the beam forming pointing position, so that a user can obtain the maximum signal-to-noise ratio of far-field receiving. FIG. 6-1 is a graph of the received power in the direction of the adjacent antenna 2 when the beam is directed to the antenna 1; fig. 6-2 is a graph of the received power in the direction of the diagonal antenna 3 when the beam is directed to the antenna 1. It can be seen that there is also interference in reception between the different antennas, which can be simply suppressed by modulation and coding as long as the receiver SNR allows. In addition, the electromagnetic wave orbital angular momentum transmission method and system based on the dimension-expanding interference code can also have the following additional technical characteristics:
because the energy of the finally transmitted OAM wave beam at the receiving end is concentrated in one direction, the signal-to-noise ratio (SNR) of the receiving end is improved by the antenna arranged at the receiving end, and the user end directly carries out demodulation and reception, thereby simplifying the structure of the receiver and reducing the complexity. As shown in fig. 4, due to the phase cancellation effect between the electromagnetic beams, the beam energy is finally converged to a point direction, and only one user data information is in the direction, and the demodulation is directly performed to send to the user side, thereby simplifying the receiver structure.
One antenna mentioned above may represent one user, and by adjusting the antenna position of the transmitter, different users may receive and transmit information at different transmission distances and different distributions, thereby facilitating distributed transmission and reception, and thus becoming a multi-user system. As a case, as shown in fig. 7, after 4 OAM mode beamforming, at the receiving end ring surface
Figure GDA0002732830580000103
A receiving antenna is arranged in the direction, and a user 1 directly receives and demodulates the data of the antenna 1; at the receiving end of the ring
Figure GDA0002732830580000104
A receiving antenna is arranged in the direction, and the data of the antenna 2 is directly received and demodulated by pointing to a user 2 after beam forming; at the receiving end the ring surface phase is
Figure GDA0002732830580000105
And
Figure GDA0002732830580000106
and a receiving antenna is arranged on the antenna, and the antenna 3 and the antenna 4 are respectively directed to the user 3 and the user 4 after beam forming and are demodulated.
In an optional embodiment, the antenna in the signal transmitting antenna module 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, the orbital angular momentum electromagnetic wave is generated using one or more of a helical phase plate, a specific reflector antenna, a specific feed antenna, a phased array antenna, a spatial light modulator, a diffraction grating, and a metamaterial.
Through the analysis, the finally emitted OAM wave beams are self-interfered to form space division light beams, the energy of each wave beam is concentrated in the direction of a corresponding receiving antenna, and the wave beams can be easily received by the corresponding antenna in the UCA, so that the signal-to-noise ratio of a receiving end is improved, and the structure of a receiver is simplified. In addition, the scheme does not need to consider the inter-modal interference, and has wide application prospect in the downlink beam forming of the multi-user OAM scheme.
In the description of the present invention, it is to be understood that the terms "central," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," "circumferential," and the like are used in the orientations and positional relationships indicated in the drawings for convenience in describing the invention and to simplify the description, and are not intended to indicate or imply that the referenced devices or elements must have a particular orientation, be constructed and operated in a particular orientation, and are therefore not to be considered limiting of the invention.
Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. In the description of the present invention, "a plurality" means at least two, e.g., two, three, etc., unless specifically limited otherwise.
In the present invention, unless otherwise expressly stated or limited, the terms "mounted," "connected," "secured," and the like are to be construed broadly and can, for example, be fixedly connected, detachably connected, or integrally formed; can be mechanically or electrically connected; they may be directly connected or indirectly connected through intervening media, or they may be connected internally or in any other suitable relationship, unless expressly stated otherwise. The specific meanings of the above terms in the present invention can be understood by those skilled in the art according to specific situations.
In the present invention, unless otherwise expressly stated or limited, the first feature "on" or "under" the second feature may be directly contacting the first and second features or indirectly contacting the first and second features through an intermediate. Also, a first feature "on," "over," and "above" a second feature may be directly or diagonally above the second feature, or may simply indicate that the first feature is at a higher level than the second feature. A first feature being "under," "below," and "beneath" a second feature may be directly under or obliquely under the first feature, or may simply mean that the first feature is at a lesser elevation than the second feature.
In the description herein, references to the description of the term "one embodiment," "some embodiments," "an example," "a specific example," or "some examples," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above are not necessarily intended to refer 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, various embodiments or examples and features of different embodiments or examples described in this specification can be combined and combined by one skilled in the art without contradiction.
Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention, and that variations, modifications, substitutions and alterations can be made to the above embodiments by those of ordinary skill in the art within the scope of the present invention.

Claims (9)

1. The utility model provides an electromagnetic wave orbit angular momentum transmission system based on dimension expansion interference code which characterized in that, includes signal transmission terminal subsystem and signal receiving terminal subsystem, wherein:
the signal transmitting terminal system comprises a data generating module, a data serial-parallel conversion module, an interference code dimension expanding module, an OAM mode selecting module and a signal transmitting antenna module which are connected in sequence,
a data generating module for receiving user data and outputting modulated serial user data;
the data serial-parallel conversion module is used for converting the serial user data into a plurality of lines of parallel data according to the OAM mode number;
the interference code dimension expanding module is used for multiplying the parallel data by an interference code, carrying out dimension expanding operation on the parallel data and changing the parallel data into a dimension expanding matrix with the same dimension as the OAM modal number, wherein the interference code is a sequence with orthogonality or quasi-orthogonality;
the OAM mode selection module is used for respectively adding elements of each column vector of the dimension expansion matrix and selecting different OAM modes to feed to uniform circular array antenna arrays of different OAM modes of the signal transmitting antenna module to form different OAM mode carrier signals;
a signal transmitting antenna module for converting different OAM mode carrier signals into space electromagnetic waves and transmitting the space electromagnetic waves,
the signal receiving terminal subsystem comprises a receiving antenna array and a data demodulation module, wherein the receiving antenna array is positioned on the same annular cross section converged by different OAM mode wave beams, each wave beam corresponds to a receiving antenna, each receiving antenna converts received space electromagnetic waves into radio frequency signals respectively and sends the radio frequency signals to the data demodulation module, the data demodulation module recovers the radio frequency signals into user data of each path,
wherein the signal transmitting antenna module includes any one of a planar coaxial UCA mode and a longitudinal coaxial UCA mode,
the planar coaxial UCA mode comprises a plurality of uniform circular antenna arrays which are coaxial in the same plane, wherein the amplitude of feed signals of the antenna arrays in the same circle is equal, the phases are sequentially uniformly delayed, different OAM modes are generated by each circle of circular antenna arrays, the radius of the uniform circular antenna arrays is calculated according to the same beam divergence angle corresponding to the different OAM modes, and different OAM mode beams are converged on a receiving antenna array positioned on the same annular section by presetting the radius of each circle of circular antenna arrays;
the longitudinal coaxial UCA mode comprises a plurality of longitudinal coaxial circular antenna arrays, each circular antenna array generates different OAM modes, beam divergence angles of the different OAM modes are calculated according to electromagnetic wave frequency 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 cross section to be converged, and different OAM mode beams are converged on the receiving antenna array located on the same annular cross section by presetting the distance between each circular antenna array and the receiving antenna array.
2. The system according to claim 1, wherein the antenna in the signal transmitting antenna module and/or the receiving antenna array is one of a horn antenna, a parabolic antenna, a cassegrain antenna, and a patch antenna.
3. The system for transmitting the orbital angular momentum of the electromagnetic wave based on the dimension-expanding interference code according to claim 1, wherein the orbital angular momentum electromagnetic wave is generated by one or more of a spiral phase plate, a specific reflector antenna, a specific feed antenna, a phased array antenna, a spatial light modulator, a diffraction grating and a metamaterial.
4. The system for transmitting the orbital angular momentum of the electromagnetic wave based on the dimension-extended interference code according to claim 1, wherein the electromagnetic wave comprises one or more of light waves, microwaves, millimeter waves and terahertz waves.
5. An electromagnetic wave orbital angular momentum transmission method based on a dimension-expanding interference code, which is characterized by applying the transmission system of claim 1 to perform the following steps:
the data generation module receives the user data and outputs modulated serial user data;
the data serial-parallel conversion module converts the serial user data into a plurality of lines of parallel data according to the number of the OAM modes;
the interference code dimension expanding module multiplies the parallel data by interference codes, performs dimension expanding operation on the parallel data to become a dimension expanding matrix with the same dimension as the OAM modal number, and the interference codes are sequences with orthogonality or quasi-orthogonality;
the OAM mode selection module adds elements of each column vector of the dimension expansion matrix respectively and selects different OAM modes to feed to the antenna arrays of the uniform circular arrays of different OAM modes of the signal transmitting antenna module to form different OAM mode carrier signals;
the signal transmitting antenna module converts different OAM mode carrier signals into space electromagnetic waves and sends the space electromagnetic waves out;
the receiving antenna array is positioned on the same annular cross section where different OAM mode wave beams converge, each wave beam corresponds to one receiving antenna, each receiving antenna converts received space transmission electromagnetic waves into radio frequency signals and sends the radio frequency signals to the data demodulation module, and the data demodulation module recovers the radio frequency signals into user data.
6. The method according to claim 5, wherein the OAM mode information received at the receiving end is aligned to different initial phases by changing the initial phases of different OAM modes generated by the signal transmitting antenna module, thereby implementing OAM beamforming pointing to different positions, and placing a receiving antenna at the beamforming pointing position to receive the radio frequency signal.
7. The method for transmitting the electromagnetic wave orbital angular momentum based on the dimension-spreading interference code as claimed in claim 5, wherein the modulation method comprises any one of amplitude keying, frequency shift keying, phase shift keying, quadrature amplitude modulation, minimum frequency shift keying, and orthogonal frequency division multiplexing modulation.
8. The method for transmitting electromagnetic wave orbital angular momentum based on the dimension-spreading interference code according to claim 5,
the signal transmitting antenna module includes a planar coaxial UCA mode,
wherein, the plane coaxial UCA mode comprises a plurality of uniform circular antenna arrays which are coaxial in the same plane, wherein, the amplitude of the feed signal of the antenna array of the same circle is equal, the phase is sequentially uniformly delayed, each circle of UCA generates different OAM modes, different OAM mode wave beams are converged on the receiving antenna array which is positioned on the same annular section by presetting the radius of each circular antenna array,
for the plane coaxial UCA mode, the radius of the uniform circular antenna array is calculated by using formula 6 according to the electromagnetic wave frequencies of different OAM modes and the same beam divergence angle,
Figure FDA0002732830570000031
formula 6 is an electric field expression of the UCA-based OAM in a spherical coordinate system (r, θ, Φ), where E is the OAM airspace electric field strength, r is the linear distance from the center of the circular array to the observation point, l is the OAM modal number, N is the number of antenna elements in the UCA, J islIs of order lA class of bessel functions that is,
Figure FDA0002732830570000032
is a wave vector, lambda is the wavelength of the electromagnetic wave, a is the radius of UCA at the transmitting end, theta is the divergence angle of the OAM wave beam,
Figure FDA0002732830570000033
9. the method for transmitting electromagnetic wave orbital angular momentum based on the dimension-spreading interference code according to claim 5,
the signal transmitting antenna module comprises a longitudinal coaxial UCA mode,
wherein, the longitudinal coaxial UCA mode comprises a plurality of same or different longitudinal coaxial circular antenna arrays, each circular antenna array generates different OAM modes, different OAM mode beams are converged on a receiving antenna array positioned on the same annular cross section by presetting the distance between each circular antenna array and the receiving antenna array,
for the longitudinal coaxial UCA mode, different beam divergence angles are calculated by using a formula 6 according to the frequency of electromagnetic waves and the radius of the uniform 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 cross section to be converged,
Figure FDA0002732830570000034
formula 6 is an electric field expression of the UCA-based OAM in a spherical coordinate system (r, θ, Φ), where E is the OAM airspace electric field strength, r is the linear distance from the center of the circular array to the observation point, l is the OAM modal number, N is the number of antenna elements in the UCA, J isl(. is a Bessel function of order I,
Figure FDA0002732830570000035
is wave vector, lambda is the electromagnetic wave wavelength, and a is half of UCA at the transmitting endThe diameter, theta, is the OAM beam divergence angle,
Figure FDA0002732830570000036
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