WO2019200803A1 - 基于数字编码超材料的直接辐射无线数字通信系统及方法 - Google Patents

基于数字编码超材料的直接辐射无线数字通信系统及方法 Download PDF

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WO2019200803A1
WO2019200803A1 PCT/CN2018/102228 CN2018102228W WO2019200803A1 WO 2019200803 A1 WO2019200803 A1 WO 2019200803A1 CN 2018102228 W CN2018102228 W CN 2018102228W WO 2019200803 A1 WO2019200803 A1 WO 2019200803A1
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matrix
metamaterial
digital communication
communication system
programmable
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PCT/CN2018/102228
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English (en)
French (fr)
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崔铁军
刘硕
白国栋
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东南大学
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Priority to EP18915261.4A priority Critical patent/EP3675283B1/en
Priority to US16/650,398 priority patent/US11165612B2/en
Priority to JP2020520805A priority patent/JP6903361B2/ja
Publication of WO2019200803A1 publication Critical patent/WO2019200803A1/zh

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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00—Baseband systems
    • H04L25/38—Synchronous or start-stop systems, e.g. for Baudot code
    • H04L25/40—Transmitting circuits; Receiving circuits
    • H04L25/49—Transmitting circuits; Receiving circuits using code conversion at the transmitter; using predistortion; using insertion of idle bits for obtaining a desired frequency spectrum; using three or more amplitude levels ; Baseband coding techniques specific to data transmission systems
    • H04L25/4906—Transmitting circuits; Receiving circuits using code conversion at the transmitter; using predistortion; using insertion of idle bits for obtaining a desired frequency spectrum; using three or more amplitude levels ; Baseband coding techniques specific to data transmission systems using binary codes
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
    • H04B7/08—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the receiving station
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q15/00—Devices for reflection, refraction, diffraction or polarisation of waves radiated from an antenna, e.g. quasi-optical devices
    • H01Q15/0006—Devices acting selectively as reflecting surface, as diffracting or as refracting device, e.g. frequency filtering or angular spatial filtering devices
    • H01Q15/0086—Devices acting selectively as reflecting surface, as diffracting or as refracting device, e.g. frequency filtering or angular spatial filtering devices said selective devices having materials with a synthesized negative refractive index, e.g. metamaterials or left-handed materials
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q15/00—Devices for reflection, refraction, diffraction or polarisation of waves radiated from an antenna, e.g. quasi-optical devices
    • H01Q15/0006—Devices acting selectively as reflecting surface, as diffracting or as refracting device, e.g. frequency filtering or angular spatial filtering devices
    • H01Q15/0013—Devices acting selectively as reflecting surface, as diffracting or as refracting device, e.g. frequency filtering or angular spatial filtering devices said selective devices working as frequency-selective reflecting surfaces, e.g. FSS, dichroic plates, surfaces being partly transmissive and reflective
    • H01Q15/002—Devices acting selectively as reflecting surface, as diffracting or as refracting device, e.g. frequency filtering or angular spatial filtering devices said selective devices working as frequency-selective reflecting surfaces, e.g. FSS, dichroic plates, surfaces being partly transmissive and reflective said selective devices being reconfigurable or tunable, e.g. using switches or diodes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q15/00—Devices for reflection, refraction, diffraction or polarisation of waves radiated from an antenna, e.g. quasi-optical devices
    • H01Q15/02—Refracting or diffracting devices, e.g. lens, prism
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q19/00—Combinations of primary active antenna elements and units with secondary devices, e.g. with quasi-optical devices, for giving the antenna a desired directional characteristic
    • H01Q19/06—Combinations of primary active antenna elements and units with secondary devices, e.g. with quasi-optical devices, for giving the antenna a desired directional characteristic using refracting or diffracting devices, e.g. lens
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q19/00—Combinations of primary active antenna elements and units with secondary devices, e.g. with quasi-optical devices, for giving the antenna a desired directional characteristic
    • H01Q19/10—Combinations of primary active antenna elements and units with secondary devices, e.g. with quasi-optical devices, for giving the antenna a desired directional characteristic using reflecting surfaces
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q3/00—Arrangements for changing or varying the orientation or the shape of the directional pattern of the waves radiated from an antenna or antenna system
    • H01Q3/44—Arrangements for changing or varying the orientation or the shape of the directional pattern of the waves radiated from an antenna or antenna system varying the electric or magnetic characteristics of reflecting, refracting, or diffracting devices associated with the radiating element
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q3/00—Arrangements for changing or varying the orientation or the shape of the directional pattern of the waves radiated from an antenna or antenna system
    • H01Q3/44—Arrangements for changing or varying the orientation or the shape of the directional pattern of the waves radiated from an antenna or antenna system varying the electric or magnetic characteristics of reflecting, refracting, or diffracting devices associated with the radiating element
    • H01Q3/46—Active lenses or reflecting arrays
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/14—Relay systems
    • H04B7/15—Active relay systems
    • H04B7/185—Space-based or airborne stations; Stations for satellite systems
    • H04B7/1851—Systems using a satellite or space-based relay
    • H04B7/18513—Transmission in a satellite or space-based system
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/14—Relay systems
    • H04B7/15—Active relay systems
    • H04B7/185—Space-based or airborne stations; Stations for satellite systems
    • H04B7/1851—Systems using a satellite or space-based relay
    • H04B7/18515—Transmission equipment in satellites or space-based relays
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L1/00—Arrangements for detecting or preventing errors in the information received
    • H04L1/0001—Systems modifying transmission characteristics according to link quality, e.g. power backoff
    • H04L1/0009—Systems modifying transmission characteristics according to link quality, e.g. power backoff by adapting the channel coding
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00—Baseband systems
    • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
    • H04L25/0202—Channel estimation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00—Baseband systems
    • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
    • H04L25/0202—Channel estimation
    • H04L25/024—Channel estimation channel estimation algorithms
    • H04L25/0242—Channel estimation channel estimation algorithms using matrix methods

Definitions

  • the invention belongs to the field of wireless communication technologies, and relates to a wireless digital communication system, and more particularly to a direct radiation wireless digital communication system based on programmable metamaterial working in a microwave frequency band.
  • Achieving this function is the digital modulation module in digital communication systems, which is the most important of the many functional modules of modern digital communication systems, which will determine the transmission rate and bit error rate of the entire system.
  • Common digital modulation methods for modern digital communication systems include amplitude keying (ASK), frequency shift keying (FSK), and phase shift keying (PSK), in which signals are separately loaded on a reference carrier (Carrier Wave). The amplitude, frequency and phase.
  • AAM Quadrature Amplitude Modulation
  • Frequency utilization is a more complex digital modulation method, which uses two mutually orthogonal carrier signals to achieve higher transmission rates and limited physical bandwidth.
  • the frequency of the digital signal in binary form is too low to be directly radiated into the space, it needs to be converted into an analog signal by a digital-to-analog conversion device (DAC), and then modulated to the RF signal by analog (RF) is then amplified by a set of RF power amplifiers (PAs) and finally radiated into free space by the transmitting antenna.
  • DAC digital-to-analog conversion device
  • PAs RF power amplifiers
  • metamaterials have been based on equivalent media, according to physics principles such as transform optics, controlling electromagnetic waves by regulating equivalent media parameters, triggering a series of peculiar physical phenomena, so they can be called "analog super Material / Analog Metamaterial".
  • Professor Cui Tiejun proposed a new type of metamaterial-electromagnetic coding and programmable metamaterial. Since the state of the unit (reflection/transmission phase) is represented by a finite number of binary values, we also call it a digital super Material/digital metamaterial.
  • the first coded metamaterial is designed in the microwave section with 1-bit coding, ie the numbers "0" and "1" are used to represent the two units with reflection phases of 0° and 180°, respectively.
  • the sequence is arranged on a two-dimensional plane to form a digital metamaterial with some regulatory functions for electromagnetic waves.
  • the assigned code sequence is a periodic arrangement of "0101"
  • the vertically incident electromagnetic wave will be split into two beams having the same pitch angle; and when the code becomes a checkerboard distribution, its radiation pattern will appear. 4 beams with the same pitch angle.
  • a 2-bit encoded metamaterial can be formed, the coding sequence can be changed, and other functions such as single beam, multibeam, and random diffuse reflection can be implemented.
  • the proposed coded metamaterial facilitates the realization of programmable metamaterials with dynamically adjustable directional patterns.
  • the "0" and “1" digital states are realized by turning on and off the diodes.
  • the field programmable gate array (FPGA) hardware system can be used to independently control each unit structure.
  • FPGA field programmable gate array
  • the coded metamaterial mentioned above successfully combines digital information with physical information; however, there is currently no wireless communication system built using digitally encoded metamaterials.
  • the present invention discloses a digitally programmable digital metamaterial-based direct radiation wireless digital communication system operating in a microwave section, which is quite different from the conventional communication system and has its own distinctive features.
  • the information transmitted on the system is loaded onto the programmable metamaterial, radiated directly into the free space under the illumination of the feed antenna, and received and aggregated by multiple receivers in the far field, which does not include traditional wireless digital communication.
  • the system's digital-to-analog conversion and modulation process and has a natural physical level of data transmission confidentiality.
  • the present invention provides the following technical solutions:
  • a direct-radiation wireless digital communication system based on digitally encoded metamaterials comprising a control module, a programmable meta-material array, and a feed antenna, the control module being coupled to a programmable meta-material control line for delivering the desired
  • the information is converted to a binary code that is loaded onto a corresponding control line of the programmable metamaterial;
  • the programmable metamaterial array includes a plurality of programmable metamaterial units for loading the binary code, which are carried under the illumination of the feed antenna
  • the binary encoding of the information is directly radiated into the free space in the form of an ever-changing far-field pattern;
  • the receiving system comprising a receiving processing module and a plurality of receivers having signal connections with the receiving processing module, the receiving system for being used in the far field
  • the electric field values received by the receiving antennas at different locations in the area are summed to obtain a far-field pattern, and the original information transmitted is recovered by the mapping relationship between the far-field pattern and the encoding sequence
  • control module is capable of dynamically adjusting the reflection/transmission phase of each cell in the programmable metamaterial array by controlling the state of the diodes in the programmable metamaterial unit through the output level.
  • the programmable metamaterial cell structure comprises an upper metal structure, an F4B dielectric layer and a metal back plate from top to bottom, and the upper metal structure comprises an H-shaped metal pattern, and the H-shaped metal pattern is provided with a diode. The diode is electrically connected to the H-shaped metal pattern.
  • the diode employs a switching diode having a switching state or a biasing diode having a continuously varying parameter.
  • the receiver includes rectennas distributed at different angles, and the receiving processing module includes an AD analog to digital conversion and a field programmable gate array FPGA processing system.
  • the receiving rectenna is configured to receive the intensity of the electric field value of the respective position, and detect the DC information; and input the signal to the receiving processing module, and the receiving processing module converts the analog value into a digital signal through AD conversion, and uses the receiving system
  • the field programmable logic array (FPGA) performs data processing to obtain discrete far field pattern data.
  • Direct radiated wireless digital communication methods based on digitally encoded metamaterials including:
  • the binary code carrying the original information will be passed to the far field in the form of a constantly changing far field pattern
  • the electric field values received by the receiving antennas at different positions in the far field region are summed to obtain a far field pattern, and the original information transmitted is recovered by the mapping relationship between the far field pattern and the encoding sequence.
  • the information to be passed is converted to a binary code and loaded onto the corresponding control line of the programmable metamaterial.
  • a communication evaluation process is further included, and the communication evaluation process includes:
  • the far field patterns corresponding to 2 N different codes are sampled at M different angles, and the obtained data is stored in a matrix A of 2 N rows and M columns;
  • a communication optimization process is further included, where the communication optimization process includes:
  • the far field pattern matrix data collected from different angles is solved to solve the Euclidean distance, and the Euclidean distance matrix D is obtained.
  • the rows and columns of all the elements larger than zero in the matrix D are output to i and j, and the matrix D is All rows containing row storage containing non-zero elements are stored in matrix b, and then it is judged whether b belongs to the available state K. If yes, continue to find the next row, if not, add b to the available state K until the end of the loop
  • the resulting K matrix includes all available states after optimization by the channel optimization algorithm.
  • Direct radiated wireless digital communication evaluation method based on digital coded metamaterial, based on digitally encoded metamaterial direct radiation wireless digital communication system including:
  • the far field patterns corresponding to 2 N different codes are sampled at M different angles, and the obtained data is stored in a matrix A of 2 N rows and M columns;
  • a direct-radiation wireless digital communication optimization method based on digitally encoded metamaterials, based on a digitally encoded metamaterial direct radiation wireless digital communication system comprising:
  • the far field pattern matrix data collected from different angles is solved to solve the Euclidean distance, and the Euclidean distance matrix D is obtained.
  • the rows and columns of all the elements larger than zero in the matrix D are output to i and j, and the matrix D is All rows containing row storage containing non-zero elements are stored in matrix b, and then it is judged whether b belongs to the available state K. If yes, continue to find the next row, if not, add b to the available state K until the end of the loop
  • the resulting K matrix includes all available states after optimization by the channel optimization algorithm.
  • the present invention has the following advantages and benefits:
  • the communication system provided by the invention eliminates the modules of digital-to-analog conversion and mixing, greatly simplifies the complexity of the communication system, and reduces the cost of the communication system.
  • the communication system provided by the present invention has an inherent security feature at the physical level, and can ensure that the transmitted information cannot be intercepted from a single point or a non-critical point from the lowest physical level, and the receiving end must receive the required reception.
  • the signal of the far field pattern at the point can successfully recover the original information, and if the far field information of one of the points is missing, the original information cannot be restored.
  • the information stealer must know each receiving location and know in real time which receiving points are being used to transmit information in order to effectively intercept the information.
  • the direct radiated wireless digital communication system proposed by the present invention can effectively increase the transmission capacity of the system by increasing the number of controllable columns of field programmable metamaterials, and is more convenient in improving performance than conventional communication methods. .
  • the system of the invention has the functions of self-adaptation and self-perception.
  • the original information transmission may be erroneous. In this case, it can be run again.
  • the communication evaluation and communication optimization procedures regain the available status and ensure smooth communication. Compared with the traditional communication system, this has greatly improved, and laid a good foundation for the self-learning communication system.
  • FIG. 1 is a structural diagram of a direct-radiation wireless communication system based on digitally encoded metamaterials, and a schematic diagram of a satellite-terrestrial communication application based on the system, which shows the structure and connection of the transmitting end of the system.
  • FIG. 2 is a schematic view showing the structure of a unit constituting a programmable metamaterial in the transmitter of the present invention, wherein (a) is a perspective view and (b) is a plan view.
  • Figure 3 shows the reflected phase and phase difference of the switching diode in the on and off states.
  • 4 is a coding pattern corresponding to the first 16 code sequences of a field programmable metamaterial having five control columns.
  • Figure 5 is a plan view of the far field of the first 16 code sequences of a field programmable metamaterial having five control columns in a plane.
  • FIG. 6 is an explanatory diagram of performance of a channel estimation algorithm and a channel optimization algorithm in a direct radiation wireless digital communication system.
  • Figure 7 is a graph showing the performance impact of a direct-radiation wireless digital communication system with nine control columns by giving different noise thresholds and sampling points quantitative analysis channel optimization algorithms.
  • Figure 8 is an example of a direct-radiation wireless digital communication system using a field-programmable supersurface with 5 control columns and 2 sampling angles.
  • the abscissa and ordinate represent the far-field electric field collected by the two sampling angles. A value.
  • 9 is a flow chart of a channel estimation method.
  • Figure 10 is a flow chart of a channel optimization method.
  • connections referred to in the present invention include all wired and wireless connection methods existing in the prior art, such as mechanical connections, electrical connections, and signal connections.
  • the direct-radiation wireless digital communication system based on digital coded metamaterial provided by the invention is composed of a transmitting system and a receiving system.
  • FIG. 1 shows an application scenario of the wireless communication system, a satellite-terrestrial communication system, and the satellite can serve as a transmitting end.
  • the ground can be equipped with many receiving devices.
  • the transmitter system includes a transmitter.
  • the transmitter is mainly composed of a field programmable gate array module (FPGA), a programmable metamaterial array, and a feed antenna.
  • the FPGA can also be replaced by other control modules with programming capabilities.
  • the receiving system includes a plurality of rectifying antennas and a receiving processing module connected to the rectifying antennas.
  • the rectifying antenna returns the received electromagnetic signals into electrical signals, and then performs analog-to-digital conversion for FPGA processing in the subsequent receiving processing modules.
  • the information to be passed is first converted to binary code "00101001" by the FPGA, and then loaded on the corresponding control line of the programmable metamaterial in a voltage manner to control the "on" of the switching diode in each control column.
  • Figure 2 shows the cell structure constituting the programmable metamaterial in the transmitter of the present invention, which is mainly composed of three parts, from top to bottom, the upper metal structure, the F4B dielectric layer and the metal back plate; the upper metal structure It is an H-shaped metal pattern; the dielectric plate has a thickness of 3 mm, a dielectric constant of 2.65, and a loss tangent of 0.001; the switching diode is soldered on the surface of the H pattern, and the two sides of the H pattern are connected to the feed line, and the entire pattern is used to adjust the phase. .
  • the coded metamaterial element is irradiated by normal incidence electromagnetic waves.
  • phase response When the diode is "on” and “off", the phase response has a phase difference of 180 degrees at 10.15 GHz, corresponding to "0" and " The digital state of 1" is shown in Figure 3.
  • the switching diode there are two different reflection/transmission phases for each cell, corresponding to 1-bit programmable metamaterials; biased diodes with continuously varying parameters can also be used, in which case there can be multiple Different reflection/transmission phases correspond to n-bits (n ⁇ 2).
  • Figures 6(a) and (b) show the far-field patterns encoded as "01010” and "00100", respectively. It can be seen that there is a significant difference between the two, which distinguishes the two far-fields. The basis for the coding sequence corresponding to the pattern is laid.
  • the present invention also provides a channel estimation method for calculating available coding states in the case of any given control column N and background noise.
  • 9 is a flow chart of a channel estimation algorithm. The working principle is briefly described as follows: First, all possible states of a programmable super surface with N control columns are encoded, and then the far field corresponding to 2 N different codes is matched. The pattern is sampled at M different angles, and the obtained data is stored in a matrix A of 2 N rows and M columns, and then the Euclidean distance D between the row vectors of the matrix A is calculated, and then the matrix D is triangulated.
  • the channel evaluation method is preferably pre-written in the control module.
  • Figure 6(d) shows the Euclidean distance matrix when the sample points are at 0°, 5°, 10°, 15°, 20° because the far-field pattern of the 1-bit programmable metamaterial is symmetric about the normal So we only sample the pattern on the normal side.
  • a certain noise threshold here set to 0.3
  • zero distance black in the figure
  • Fig. 6(g) The sampling point in Fig. 6(g) is the same as Fig. 6(d), but the noise The threshold is raised to 0.6, and it can be clearly seen that the originally darker pixel point (closer distance) in Fig. 6(d) becomes black (zero distance) in Fig. 6(g), which is found by using the channel estimation algorithm.
  • the number of available states is only one. This is due to the fact that there are too many zero elements in the matrix. Many states are connected to each other, causing the system to fall into the worst state and cannot transmit any information.
  • the present invention proposes a channel optimization algorithm that increases the number of available coding states by discarding some coding states.
  • the far field pattern matrix data collected at different angles is solved by solving the Euclidean distance, and the Euclidean distance matrix D is obtained, and all the matrices in the matrix D are greater than zero.
  • the row and column where the element is located are output to i and j, and all the rows in the matrix D containing the non-zero element row are stored in the matrix b, and then it is judged whether b belongs to the available state K, and if so, the search continues.
  • the K matrix is all available states after optimization by the channel optimization algorithm.
  • FIG. 8(a) shows the position of 16 coding states in a two-dimensional coordinate system when the sampling points are at 10° and 30°. It can be seen that the coding states 16, 9, 8, 12, 13, 14 The coordinates are the same as the states 2, 3, 4, 6, 7, and 10, respectively. At this time, if a noise threshold G is set to the system, any two coding states whose distances are smaller than G in the figure will be regarded as the same coding state because they cannot be distinguished.
  • the sampling angle is changed to 20° and 40°, and the coordinate positions of the 16 coding states are changed, as shown in Fig. 8(b).
  • the noise threshold G is still 0.3.
  • the channel optimization process is performed on the Euclidean distance matrix, it can be found that if the state 2, 4/8, 5 is deleted, four available coding states can be obtained, namely 1, 3/9, 6/ respectively. 12, 7/13.
  • changing the position of the sample points will help increase the number of available coding states after optimization.
  • the noise threshold G is reduced to 0.1, and the sampling angle is consistent with the first example.
  • the number of available coding states is 9, which are 1, 2/16, respectively. , 3/9, 4/8, 5, 6/12, 7/13, 10/14, 11, but since these encoding states are independent of each other at this time, there is no encoding state and two other encoding states are connected at the same time. Therefore, in this case, the channel optimization algorithm cannot add any available state.
  • FIG. 7(a) shows the number of available coding states for the system (square mark) and after (circular mark) system before using the optimization method, where the horizontal axis is the noise threshold.
  • the above example demonstrates the important role of the channel optimization method in increasing the system's transmission rate.
  • the abscissa indicates the number of sampling points at intervals of 1° from 0° (normal direction), for example, 30 indicates that there is one receiver every 1° from 1° to 30°. All curves have been processed by the channel optimization method. It can be seen from Fig. 7(b) that all the curves increase with the increase of the number of sampling points.
  • the noise threshold When the noise threshold is set to 0.1, the number of available coding states increases rapidly when the number of sampling points is from 1 to 15, when the number of sampling points reaches 19 At this point, the system reaches the maximum available state number of 72, which means that when the number of sample points exceeds a certain key point, the number of available states of the system will be saturated and no longer grow.
  • the system is in a low background noise environment, only a small number of sample points are needed to achieve optimal conditions. As we continue to raise the noise threshold to 0.3 and 0.5, this key point will increase to 28 and 40 respectively; however, when the noise threshold continues to rise to 0.7 and 0.9, the number of available states of the system drops dramatically, even when the number of samples reaches 90. , also can not achieve the best state. However, in this high background noise state, the channel optimization algorithm will still effectively increase the number of available states.
  • MIMO systems Since direct-radiation wireless digital communication systems also employ multiple receivers, researchers may prefer to classify them with MIMO systems. It is important to note that they are essentially two completely different wireless communication systems.
  • the MIMO system utilizes multiple transmitters and multiple receivers to fully utilize the multipath effects of electromagnetic waves, thereby increasing system capacity and reliability, while direct radiating wireless digital communication systems do not require the use of multiple transmitters.
  • the reason why MIMO systems must use multiple transmitters is because it needs to transmit multiple low-rate information streams through different antennas to obtain the maximum spatial diversity gain.
  • this method still belongs to modern digital communication systems. The information is still modulated on the carrier in amplitude, frequency or phase.
  • the distance between receivers usually only needs to maintain half or one wavelength to satisfy the low correlation between signals, but in direct radiated wireless digital communication systems, the receiver needs to span the entire distance.
  • the field pattern has a much larger spacing than the distance between receivers in a MIMO system.
  • the most important difference is that for direct-radiation wireless digital communication systems, the information is modulated on the far-field pattern of the field-programmable super-surface antenna, and the baseband digital signal can be directly field-programmable in digital form without modulation.
  • the super-surface antenna is radiated into the free space under the illumination of the feed, so the direct radiation wireless digital communication system is greatly simplified in the system architecture compared to the modern digital communication system.
  • the novel communication system proposed by the present invention is an adaptive (having cognitive and self-aware function) system capable of coping with different wireless communication situations such as occlusion and multipath.
  • direct-radiation wireless digital communication systems operate in the frequency domain and the required bandwidth is extremely narrow, it is believed that the development of a dual-band or even multi-band field-programmable super-surface will facilitate higher-speed information transmission.
  • Another advantage of direct-radiation wireless digital communication systems over modern digital communication systems is the support for higher-order modulation, where the system can achieve higher transmission rates at the same symbol rate (baud rate), resulting in higher Spectrum utilization.
  • the highest modulation method usually used is QPSK, that is, 2 bits of information are transmitted in one symbol period. .
  • higher order can be obtained by increasing the number of controllable columns of field-programmable super-surfaces while deploying more dense ground stations on the Earth to obtain higher-resolution far-field patterns.
  • the modulation rate of the number is believed to be easy to achieve 8-bit/symbol high-order modulation through engineering optimization, and the transmission rate will be at least 4 times higher than the QPSK modulation method. If this is based on the dual-band field programmable super surface It will achieve an eightfold increase, which will bring a revolutionary breakthrough in satellite-earth data transmission rates.
  • Another distinctive feature of direct-radiation wireless digital communication systems is their natural security features, which ensure that the information conveyed cannot be intercepted from a single point or non-critical point from the lowest physical level, which is required by traditional communication methods.
  • a large number of software encryption algorithms are used to protect information security. This is because the transmitted information is dispersed at different angles of the far-field pattern, and the receiving end can recover the transmitted data only by simultaneously and completely acquiring the data at the specified sampling point, and if one of the points is missing Field information will not be able to restore the original information.

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Abstract

本发明公开了一种基于数字可编程超材料的直接辐射无线数字通信系统，包括发射系统和接收系统，发射系统所传递的信息被加载到可编程超材料上面，在馈源天线的照射下以不断变换的远场方向图的形式直接地辐射到自由空间中；接收系统将处于远场区不同位置处的接收天线接收到的电场值汇总得到远场方向图，并通过远场方向图与编码序列之间的映射关系恢复出所发送的原始信息。本发明提供的通信系统省去了数模转换以及混频的模块，大大简化了通信系统的复杂度，降低了通信系统的成本；具有与生俱来的保密特性，能够从最底层的物理层面保证所传递的信息无法从单点或者非关键点截获，易于提升性能，且具有自适应、自我感知等能力。

Description

基于数字编码超材料的直接辐射无线数字通信系统及方法 技术领域
本发明属于无线通信技术领域，涉及一种无线数字通信系统，更为具体的说，是涉及一种工作在微波频段的基于可编程超材料的直接辐射无线数字通信系统。
背景技术
随着电报、电话的发明，以及电磁波的发现，人类通信的方式发生了根本性的变革，人们利用金属导线上的电脉冲来进行有线信息传递，通过电磁波来进行无线通信。当今通信领域的迅猛发展得益于数字通信系统的出现，现代数字通信系统的工作原理大致如下：首先将所要传递的信息转换为数字形式(二进制码)，这样便于计算机等电子设备进行存储和后处理。致力于数字通信的研究者们一直以来都在关注如何将信息有效地编码和调制，使得信息能够以最小的误码率抵达接收端。实现这一功能的是数字通信系统中的数字调制模块，这是现代数字通信系统众多功能模块中最重要的一个，它将决定整个系统的传输速率和误码率。现代数字通信系统的常用数字调制方法包括振幅键控(ASK)、频移键控(FSK)和相移键控(PSK)，在这些调制方法中，信号被分别加载在参考载波(Carrier Wave)的幅度、频率和相位上。除此之外，还有一种更为复杂的数字调制方法—正交振幅调制(QAM)，它采用两个互相正交的载波信号，因此能够在有限的物理带宽内获得更高的传输速率和频率利用率。由于二进制形式的数字信号的频率太低，无法被直接辐射到空间中，因此需要通过一个数字— 模拟转换器件(DAC)先将它转换为模拟信号,随后再通过模拟的方式调制到射频信号(RF)上，然后通过一组射频功率放大器(PA)进行功率放大，最后被发射天线辐射到自由空间中。
过去15年以来，超材料一直以等效媒质为基础，根据变换光学等物理学原理，通过调控等效媒质参数而控制电磁波，引发一系列奇特的物理现象，因此可将它们称为“模拟超材料/模拟超材料”。2014年，崔铁军教授提出一种新型的超材料—电磁编码与可编程超材料，由于其单元的状态(反射/透射相位)采用有限个二进制数值来表示，因此我们也将其称为数字超材料/数字超材料。首个编码超材料设计在微波段，具有1-比特编码，即采用数字“0”和“1”来分别代表反射相位为0°和180°的两种单元，通过将两种单元按照预定设计的序列排列在二维平面上，便形成了对电磁波具有某种调控功能的数字超材料。例如，当所赋予的编码序列为周期排列的“0101…”时，垂直入射的电磁波将被分为两个具有相同俯仰角的波束；而当编码变为棋盘格分布时，其辐射方向图将出现4个具有相同俯仰角波束。通过将360°相位四等分，可形成2-比特的编码超材料，改变编码序列，还可实现其他诸如单波束、多波束和随机漫反射等功能。编码超材料的提出为实现具有动态可调方向图的可编程超材料提供了便利，通过设计加载开关二极管的单元结构，利用导通和关闭二极管来实现“0”和“1”数字态的电调控，便可采用现场可编程门阵列(FPGA)硬件系统对每个单元结构中进行独立调控，通过给予可编程超材料不同的编码序列，可实现对电磁波动态实时地功能调控。
以上所提到的编码超材料成功地将数字信息与物理信息有机地结合了起来；但目前，尚无利用数字编码超材料所搭建的无线通信系 统。
此外，在实际无线通信系统中，噪声无处不在，如何对抗噪声是无线通信系统中的一大关键性技术，并将决定系统的信道质量和传输速率，在传统无线数字通信系统的研究历程中，已涌现出多种不同的技术和手段来克服或减小噪声对通信系统的影响，其中改善信道较为有效的一个途径是提高系统的信噪比(SNR)，这可以通过提升发射机的输出功率或者采用多输入多输出技术(MIMO)来实现，但是这两种方案是以额外的功耗需求和更高的系统复杂度为代价的，在诸如卫星等对功耗敏感的设备上是不可行的。在现有技术中，还未出现针对基于超材料的无线通信系统在噪声环境下的信道优化方法。
发明内容
为解决上述问题，本发明公开了一种工作在微波段的基于数字可编程数字超材料的直接辐射无线数字通信系统，其与传统的通信系统大不相同，有着自身鲜明的特点。在本系统上所传递的信息被加载到可编程超材料上面，在馈源天线的照射下直接地辐射到自由空间，被远场的多个接收机接收并汇总，其中不包含传统无线数字通信系统的数模转换以及调制过程，并且具有天然的物理层面的数据传输保密性。
为了达到上述目的，本发明提供如下技术方案：
基于数字编码超材料的直接辐射无线数字通信系统，所述发射系统包括控制模块、可编程超材料阵列和馈源天线，所述控制模块与可编程超材料控制线相连，用于将所需传递的信息转换为二进制码，加 载在可编程超材料相应的控制线上；可编程超材料阵列包含若干可编程超材料单元，用于加载所述二进制码，在馈源天线的照射下这些携带有信息的二进制编码以不断变换的远场方向图的形式直接地辐射到自由空间；所述接收系统包括接收处理模块以及与接收处理模块具有信号连接的若干接收机，接收系统用于将处于远场区不同位置处的接收天线接收到的电场值汇总得到远场方向图，并通过远场方向图与编码序列之间的映射关系恢复出所发送的原始信息。其中控制模块利用现场可编程门阵列FPGA将所传递的信息转换为二进制码，以高低电平的方式加载在可编程超材料相应的控制线上。
进一步的，所述控制模块能够通过输出电平调控可编程超材料单元中二极管的状态，进而动态地调控可编程超材料阵列中每个单元的反射/透射相位。
进一步的，所述可编程超材料单元结构从上至下包括上层金属结构、F4B介质层和金属背板，上层的金属结构包括H形金属图案，所述H形金属图案中设置有二极管，所述二极管与H形金属图案具有电连接。
进一步的，所述二极管采用具有开关状态的开关二极管或具有参数连续变化的偏压二极管。
进一步的，所述接收机包括分布在不同角度的整流天线，接收处理模块包括AD模数转换以及现场可编程门阵列FPGA处理系统。所述接收整流天线用于接收各自所处方位的电场值强度，并且检波形成直流信息；再将其输入给接收处理模块，接收处理模块通过AD转换将 模拟值转换成数字信号，并利用接收系统中的现场可编程逻辑阵列(FPGA)进行数据处理，得到离散的远场方向图数据。
基于数字编码超材料的直接辐射无线数字通信方法，包括：
将携带有原始信息的二进制编码将以不断变换的远场方向图的形式传递到远场区；
将处于远场区不同位置处的接收天线接收到的电场值汇总得到远场方向图，并通过远场方向图与编码序列之间的映射关系恢复出所发送的原始信息。
进一步的，在传递二进制编码之前还包括：
将所需传递的信息转换为二进制码，加载在可编程超材料相应的控制线上。
进一步的，还包括通信评估过程，所述通信评估过程包括：
首先对一个具有N个控制列的可编程超表面所有的可能状态进行编码；
然后对着2 N个不同的编码对应的远场方向图在M个不同的角度上进行采样，得到的数据存储在一个2 N行M列的矩阵A中；
随后计算矩阵A各个行向量之间的欧氏距离D，之后将矩阵D下三角化，并将所有小于噪声门限的元素置0，其他元素置1，形成新的矩阵D’，最后寻找D’中不含0元素的行标号，并输出到矩阵K中，即得到最终得到的可用状态的编码。
进一步的，在通信评估过程之后还包括通信优化过程，所述通信优化过程包括：
首先将不同角度采集到的远场方向图矩阵数据进行求解欧氏距离，得到欧氏距离矩阵D，将矩阵D中所有大于零的元素所在的行和列输出到i和j，将矩阵D中所有包含非零元素的行存储对应的行存储到矩阵b中，接下来判断b是否属于可用状态K，如果是则继续找下一行，如果不是则将b添加到可用状态K中，直至循环结束得到的K矩阵即包括经信道优化算法优化之后的所有可用状态。
基于数字编码超材料的直接辐射无线数字通信评估方法，基于数字编码超材料的直接辐射无线数字通信系统实现，包括：
首先对一个具有N个控制列的可编程超表面所有的可能状态进行编码；
然后对着2 N个不同的编码对应的远场方向图在M个不同的角度上进行采样，得到的数据存储在一个2 N行M列的矩阵A中；
随后计算矩阵A各个行向量之间的欧氏距离D，之后将矩阵D下三角化，并将所有小于噪声门限的元素置0，其他元素置1，形成新的矩阵D’，最后寻找D’中不含0元素的行标号，并输出到矩阵K中，即得到最终得到的可用状态的编码。
基于数字编码超材料的直接辐射无线数字通信优化方法，基于数字编码超材料的直接辐射无线数字通信系统实现，包括：
首先将不同角度采集到的远场方向图矩阵数据进行求解欧氏距离，得到欧氏距离矩阵D，将矩阵D中所有大于零的元素所在的行和列输出到i和j，将矩阵D中所有包含非零元素的行存储对应的行存储到矩阵b中，接下来判断b是否属于可用状态K，如果是则继续找 下一行，如果不是则将b添加到可用状态K中，直至循环结束得到的K矩阵即包括经信道优化算法优化之后的所有可用状态。
与现有技术相比，本发明具有如下优点和有益效果：
1、与传统的通信系统相比，本发明提供的通信系统省去了数模转换以及混频的模块，大大简化了通信系统的复杂度，降低了通信系统的成本。
2、本发明提供的通信系统在物理层面具有与生俱来的保密特性，能够从最底层的物理层面保证所传递的信息无法从单点或者非关键点截获，接收端必须接收到所需接收点处的远场方向图的信号，才能顺利地恢复出原始信息，而如果缺失其中某一点的远场信息，将无法还原原始信息。信息窃取者必须获知每一个接收位置，并且实时知道哪些接收点正在用来传输信息，才能有效截取信息。
3、本发明所提出的直接辐射无线数字通信系统，可通过增加现场可编程超材料的可控列数，来有效地提升系统的传输容量，在提升性能方面，较传统的通信方式更为简便。
4、基于信道评估以及信道优化算法，本发明系统具有自适应、自我感知等能力，当该系统处于外界干扰的情况下，原有的信息传输会发生误码，这种情况下，可以再次运行通信评估以及通信优化程序，重新获得可用状态，保证通信顺畅进行。这相比于传统的通信系统有了较大的提升，也为具有自我学习的通信系统奠定了良好的基础。
附图说明
图1为本发明提供的基于数字编码超材料的直接辐射无线通信 系统结构图，以及基于本系统的卫星—地面通讯应用的原理示意图，其中展示出了系统发射端的结构和连接。
图2为构成本发明发射机中可编程超材料的单元结构示意图，其中(a)为立体图，(b)为俯视图。
图3为开关二极管在开和关状态下所对应的反射相位及相位差。
图4为具有5个控制列的现场可编程超材料的前16个编码序列对应的编码图案。
图5为具有5个控制列的现场可编程超材料的前16个编码序列在平面内的远场方向图。
图6为直接辐射无线数字通信系统中信道评估算法和信道优化算法的性能表现的说明图。
图7为通过给定不同的噪声门限和采样点数定量分析信道优化算法对一个具有9个控制列的直接辐射无线数字通信系统的性能影响。
图8为采用具有5个控制列的现场可编程超表面和2个采样角度的直接辐射无线数字通信系统示例，图中横坐标和纵坐标分别代表两个采样角度所采集到的远场电场归一化值。其中(a)采样角度为10°和30°，噪声门限G＝0.3；(b)采样角度为20°和40°，噪声门限G＝0.3；(c)采样角度为10°和30°，噪声门限G＝0.1。
图9为信道评估方法流程图。
图10为信道优化方法流程图。
具体实施方式
以下将结合具体实施例对本发明提供的技术方案进行详细说明，应理解下述具体实施方式仅用于说明本发明而不用于限制本发明的范围。本发明中所指的连接包含机械连接、电连接、信号连接等现有技术中已有的所有有线、无线连接方式。
本发明提供的基于数字编码超材料的直接辐射无线数字通信系统由发射系统和接收系统构成，图1所示的是该无线通信系统的一个应用场景，卫星—地面通讯系统，卫星可以作为发射端，地面可以布置很多接收装置。发射系统中包括一台发射机，发射机主要由现场可编程门阵列模块(FPGA)、可编程超材料阵列、馈源天线组成，FPGA也可以替代为其他具有编程能力的控制模块。接收系统包括多个整流天线以及与这些整流天线连接的接收处理模块，整流天线将接收到的电磁信号返回成电信号，再进行模数转换，以便后面的接收处理模块之中的FPGA处理。所需传递的信息首先被FPGA转换为二进制码“00101001...”，随后以电压的方式加载在可编程超材料的相应的控制线上，用于控制每一个控制列中开关二极管的“开”与“断”状态，进而动态地调控可编程超材料阵列中每个单元的反射/透射相位；在馈源天线的照射下，这些携带有原始信息的二进制编码将以不断变换的远场方向图的形式传递到远场区，处于远场区不同位置处的整流天线将各自接收到的电场值强度发送给接收处理模块，随后接收处理模块通过汇总多个整流天线的数据，得到离散的远场方向图数据，最后根据远场方向图和可编程超材料的编码序列之间的映射关系恢复出 所发送的原始信息。
图2给出了构成本发明中发射机中的可编程超材料的单元结构，其主要由三部分组成，从上至下依次是上层金属结构、F4B介质层和金属背板；上层的金属结构为H形状金属图案；介质板厚度为3mm，介电常数2.65，损耗角正切为0.001；开关二极管焊接在H图形表面，H图形的两边延伸与馈源线相连接，整个图形协同用来调节相位。在二极管的开关状态下，该编码超材料单元在正入射电磁波照射下，当二极管处于“开”和“断”时，相位响应在10.15GHz有180度的相位差，分别对应“0”与“1”的数字状态，如图3所示。基于开关二极管，此时每个单元存在两个不同的反射/透射相位，对应于1-比特可编程超材料；也可以采用具有参数连续变化的偏压二极管，此时每个单元可存在多个不同的反射/透射相位，对应于n-比特(n≥2)。
为了说明本发明所提出的直接辐射无线通信系统的工作原理，这里给出一个拥有5个控制列的1-比特现场可编程超材料，固定第一列编码为0，其余四列编码可任意为0或者1，图4给出了所有可能的编码图案。基于FFT快速算法，可以得到编码图案在平面内的远场方向图，如图5所示。
图6(a)和(b)分别给出了编码为“01010”和“00100”的远场方向图，可以看出这两者之间存在显著的差异，这为我们区分这两个远场方向图所对应编码序列奠定了基础。
本发明还提供了信道评估方法，用于计算任意给定控制列N和背景噪声的情况下的可用编码状态。图9是信道评估算法的流程图，其 工作原理简要介绍如下：首先对一个具有N个控制列的可编程超表面所有的可能状态进行编码，然后对着2 N个不同的编码对应的远场方向图在M个不同的角度上进行采样，得到的数据存储在一个2 N行M列的矩阵A中，随后计算矩阵A各个行向量之间的欧氏距离D，之后将矩阵D下三角化，并将所有小于噪声门限(NoiseG)的元素置0，其他元素置1，形成新的矩阵D’，最后寻找D’中不含0元素的行标号，并输出到矩阵K中，矩阵K即是最终得到的可用状态的编码。信道评估方法优选预写在控制模块中。
为了定量地计算出图5中每个远场方向图之间的差异，我们分别计算每两个方向图之间的欧氏距离，并将其绘制在图6(c)中，其中，每个像素(m,n)的灰度值代表第m个和第n个远场方向图之间的相对欧式距离，位于(16,2)、(9,3)、(8,4)、(12,6)、(13,7)、(14,10)的六个黑色的像素表示他们之间的距离为零，也就意味着这6组远场方向图两两之间完全一致，不可区分。对于本例，能够用于进行无歧义信息传输的编码状态有10个，分别为图5中第(1,2,3,4,5,6,7,10,11,15)个编码序列，如果我们从中任意挑选8个，便可以3比特/码元的速率进行信息传输。
在实际应用中，我们并不需要、同时也无法完全获取诸如图6(a)和(b)中的-90°到90°之间的整个远场方向图。在卫星-地球通讯应用中，接收到的远场方向图的最大的角度(与超材料法线夹角)取决于卫星距地高度，虽然对于低轨道卫星来说，这一角度可以达到80度，然而对于超过60°的大角度内所接收到的信号，相比小角度 处的信号存在严重的信号时延和衰减，这些因素会降低系统传输速率。鉴于这个考虑，我们仅对0-30度之间的远场方向图进行离散采样，如图6(a)和(b)中不同颜色直线处所对应的角度所示。图6(d)给出了当采样点位于0°、5°、10°、15°、20°时的欧氏距离矩阵，因为1-比特可编程超材料的远场方向图关于法线对称，因此我们只对法线一侧的方向图进行采样。考虑到实际应用中，地面站的接收灵敏度以及不可避免的背景噪声干扰，我们将距离矩阵中距离小于一定噪声门限(这里设定为0.3)的距离像素点认为是零距离(在图中以黑色像素点标出)。从图6(d)中可以看出，可用的编码状态降低为6个，分别是第1、2、3、4、6、7，任选其中4个状态，便可支持2比特/码元的传输速率。如果我们继续减少采样点，仅在0°、10°、20°进行采样，可以预见，距离矩阵中的平均距离将进一步减小，这可以从图6(e)中看出，其中矩阵的整体灰度值明显比图6(c)和(d)要小，但此时的可用编码状态数仍然为6个，这说明减少采样点并不一定导致更少的可用编码状态数，但可以确定的是，增加采样点或者扩大采样角度范围，可有效地增加整个欧氏距离矩阵的平均距离，使得系统拥有更好的抗噪性能，这点可进一步从图6(f)中得以印证，这次采样角度为0°、5°、10°、15°、20°、25°、30°，图6(f)中的距离矩阵的灰度值明显要高于图6(d)和(e)。
考虑到实际应用中可能面对的高噪声环境，需要进一步考量直接辐射无线数字通信系统在较高噪声门限下的表现，图6(g)中的采样 点与图6(d)相同，但是噪声门限提升至0.6，可以明显看出图6(d)中原本较暗的像素点(较近的距离)在图6(g)中变为黑色(零距离)，通过采用信道评估算法，发现此时的可用状态数仅为1，这是由于矩阵中存在太多的零元素，很多状态互相连接在一起，导致系统陷入最差的状态，无法传输任何信息。在这种情形下，需要寻找一种类似数字通信中的信道编码算法，即在不提升系统信噪比的情况下，增加直接辐射无线通信数字系统的可用编码状态，进而提高传输速率。本发明提出一种信道优化算法，通过舍弃一些编码状态来增加可用编码状态数。
图10是信道优化算法的流程图，其工作原理简要介绍如下：首先将不同角度采集到的远场方向图矩阵数据进行求解欧氏距离，得到欧氏距离矩阵D，将矩阵D中所有大于零的元素所在的行和列输出到i和j，将矩阵D中所有包含非零元素的行存储对应的行存储到矩阵b中，接下来判断b是否属于可用状态K，如果是则继续找下一行，如果不是则将b添加到可用状态K中，循环结束时，K矩阵便是经信道优化算法优化之后的所有可用状态。
下面，将通过二维情况(即仅存在两个采样点)来阐述信道优化算法的工作原理。
这里仍然以图4中相同的具有5个控制列的现场可编程超表面，当仅采用两个采样点时，每个编码对应的采样数据便可以简单地表示在如图8所示二维直角坐标系中，它们之间的欧氏距离也将可以直观地从图中读出。图8(a)给出了当采样点位于10°和30°时，16个 编码状态在二维坐标系中的位置，可以看出，其中编码状态16、9、8、12、13、14分别与状态2、3、4、6、7、10的坐标相同。这时，如果给系统设定一个噪声门限G，图中距离小于G的任意两个编码状态将由于无法区分而被视为同一个编码状态。由于所有的编码状态互相之间的距离均小于0.3，所以当G＝0.3时，所有编码状态都将无法区分，被视为同一个状态，此时将无法传递任何信息。如果在图8(a)中以状态1和5为圆心，以0.3为半径各画一个圆，将可发现状态3/9同时落在两个圆内，它的存在导致状态1和5连接在一起而无法区分，因此可以很自然的想到，若将状态3/9删去，状态1和5的连接也就断开了，它们两者之间将可以互相区分，系统将可以以1-比特/码元的速率进行传输。仔细观察图8(a)，可以发现还存在其他的组合，用于支持1-比特/码元的传输，如2/16和11，4/8和10/14，5和4/8等。然而，在G＝0.3的噪声门限下，无论怎样优化，只能获得最多两个可用的编码状态，继续增加可用编码状态数的唯一办法就是降低噪声门限，也就等同于提升系统信噪比。
在第二个示例中，将采样角度改为20°和40°，16个编码状态的坐标位置了发生改变，如图8(b)所示，与上例相同，当噪声门限G仍为0.3时，只有一个可用编码状态，如果对欧式距离矩阵进行信道优化处理，可发现如果删除状态2、4/8、5，便可得到4个可用编码状态，分别是1、3/9、6/12、7/13。从本例可以看出，改变采样点的位置，将有助于增加优化后的可用编码状态数。在图8(c)所示的第三个示例中，将噪声门限G减小至0.1，采样角度与第一示例 保持一致，这时可用编码状态数为9个，分别是1、2/16、3/9、4/8、5、6/12、7/13、10/14、11，但由于此时这些编码状态都是互相独立，不存在某个编码状态同时连接另两个编码状态，因此这样的情况，信道优化算法无法增加任何可用状态。
在了解了信道优化算法的工作原理后，通过对图6(g)中的距离矩阵进行信道优化处理，我们获得了4个可用编码状态，分别为1、3、4、11，此时仍然可支持与图6(d)中一样的2-比特/码元的传输速率。我们在图6(h)中给出了此时4个编码状态的欧式距离矩阵，可以看出所有矩阵均明显大于零。可见，信道优化方法能够非常有效地提高直接辐射无线通信系统的传输速率。
由于卫星—地球通信中往往更倾向于高比特率传输速率，因此这里需要进一步对信道优化方法做深入分析，通过对基于9个控制列的直接辐射无线通信系统设定不同的噪声门限和采样分辨率，来定量考察信道优化算法对可用状态编码数的提升能力，此时采样角度设定在0°、5°、10°、15°、20°。图7(a)展示了在使用优化方法之前(方形标记)和之后(圆形标记)系统的可用编码状态数，其中横轴为噪声门限值。可以清楚的看出，当噪声门限从0.1增加至0.3时，两条曲线均快速下降，说明对于优化方法处理前后，均存在一个明显的噪声门限，使得系统的可用编码状态数迅速下降。但是，当我们采用信道优化方法后，噪声为0.3-0.67区间的可用状态数增加了至少4倍，当噪声门限为0.41时，增长幅度达到最大(可用状态数为12)，而此时未采用信道优化方法时仅有一个可用状态，无法传输任何数 据，这个提升幅度等效于增加了2-3倍传输速率。进一步观察优化过的编码状态数可以发现，在图中所给出的噪声门限范围内，支持至少1-比特/码元的传输速率，而当噪声门限不是很大的情况下(<0.72)将支持2-3比特/码元的传输速率。
上述例子展示了信道优化方法在提升系统传输速率方面的重要作用，这里我们将通过给出不同噪声门限时的可用编码数的曲线来分析采样点数对系统性能的影响，如图7(b)所示，其中横坐标表示从0°(法线方向)算起的、间隔为1°采样点数，例如30表示从1°到30°每隔1°有一个接收机。所有曲线都已经过信道优化方法处理。从图7(b)可以看出，所有曲线都随着采样点数的增加而增加，当噪声门限设置为0.1时，可用编码状态数在采样点数从1-15时迅速增长，当采样点数达到19时，系统就达到了最大可用状态数72，这意味着当采样点数超过某个关键点时，系统的可用状态数将达到饱和而不再增长。当系统处于低背景噪声环境中时，仅需要少量采样点便可达到最佳状态。当我们继续将噪声门限提升到0.3和0.5时，这个关键点将分别增长至28和40；然而当噪声门限继续提升到0.7和0.9时，系统的可用状态数急剧下降，即使当采样点数达到90，也无法实现最佳状态。但是，在这种高背景噪声状态下，采用信道优化算法仍将有效提升可用状态数。
为了同时评价噪声门限和采样数对系统性能的影响，我们在图7(c)和(d)中给出了可用编码状态数在噪声门限值和采样数中的二维图，其中图7(c)为未采用信道优化算法，图7(d)为经过信道 优化算法处理之后，此时系统的控制列数仍为9列。显然，当我们增加采样点数时，两种情况下的可用编码数都在增加，噪声门限越低，达到最佳状态所需的采样点数越少。对于未经采用优化算法的情况,当采样点数小于20时，可用编码状态数非常有限(见图7(c)中紫色部分)，并且从最佳状态到最差状态的变化非常迅速，造成一个明显的边界。当采用信道优化方法后，可用编码状态数得到的显著的提升，图7(c)中原本紫色的部分在图7(d)中变为了黑色，说明信道优化算法可以减缓系统从最佳状态到最差状态的变化范围，减小系统对噪声和采样点数的敏感性。
将信道评估方法和信道优化方法集成到FPGA控制系统之中，就可以在各种环境中或者在受到外界干扰的情况下，迅速做出反应，进而检测出可用的编码状态，有效地保障通信速率及通信质量。
由于直接辐射无线数字通信系统同样采用多个接收机，研究者们可能倾向于将它与MIMO系统归为一类，这里需要指出，它们本质上属于两种完全不同的无线通信系统。MIMO系统是通过采用多个发射机和多个接收机来充分利用电磁波的多径效应，进而提高系统容量和可靠性，而直接辐射无线数字通信系统并不需要采用多个发射机。MIMO系统必须采用多个发射机的原因是因为它需要将多条低码率的信息流通过不同的天线发射出去，以获得最大的空间分集增益，然而这种方式仍然归属于现代数字通信系统，信息仍然以幅度、频率或相位的方式调制在载波上。另外，在MIMO系统中，接收机之间的距离通常仅需要保持半个或者一个波长即可满足信号之间的低相关性，但 是在直接辐射无线数字通信系统中，接收机需要横跨整个远场方向图，其间距远大于MIMO系统中的接收机之间的距离。最重要的一个区别是，对于直接辐射无线数字通信系统，信息是调制在现场可编程超表面天线的远场方向图上，并且基带数字信号无需调制便可直接以数字的形式作用于现场可编程超表面天线，进而在馈源的照射下辐射到自由空间中，因此直接辐射无线数字通信系统相比现代数字通信系统，在系统架构上得到了大幅度的简化。需要指出的是，在本文中，虽然以卫星—地球通信为例对直接辐射无线数字通信系统进行分析讨论，但这并不意味着它只能在这种视距传播情形下工作。在实际应用中，应当考虑到发射机和接收机的近场区域由于存在物体遮挡而导致远场方向图发生变化的可能性，或者传播信道中由于各种因素所导致的信号衰减，但是这并不影响直接辐射无线数字通信系统的正常工作，可利用信道评估方法和信道优化方法，提升系统性能。在系统搭建完成后使用之前，应经过信道评估和对接收系统的反复调整来确定最佳位置、角度和参数。当评估结果不满足需求时，采用信道优化方法来增加可用编码状态。还可以对信道进行实时地评估和优化，实时更新可用编码状态，使系统实时处于最大传输速率。本发明所提出的全新的通信系统是一种能够应对遮挡、多径等不同无线通信情形的自适应(具有可认知和自我感知功能)系统。
由于直接辐射无线通信系统工作在频域，所需的带宽极窄，相信通过研制双频段甚至多频段现场可编程超表面，将有助于实现更高速率的信息传输。直接辐射无线数字通信系统相比于现代数字通信系统 的另一个优势是对高阶调制支持，即系统能够在相同的码元速率(波特率)下实现更高的传输速率，获得更高的频谱利用率。对于星地传输这样信噪比通常较低的应用场景，为了将误码率(BER)控制在一定范围内，通常采用的最高调制方式就是QPSK，也就是说一个码元周期内传输2比特信息。而对于直接辐射无线数字通信系统，通过增加现场可编程超表面的可控列数，同时在地球上部署更加密集的地面站来获取更高分辨率的远场方向图，将可获得更高阶数的调制率，相信通过工程优化，可轻松达到8-比特/码元的高阶调制，传输速率将比QPSK调制方式高出至少4倍，如果在这个基础上采用双频段现场可编程超表面，将可达到8倍的提升，这将带来卫星—地球数据传输速率的革命性突破。
直接辐射无线数字通信系统另一个与众不同的特点是其天然的保密特性，其从最底层的物理层面保证了所传递的信息无法从单点或者非关键点截获，这与传统的通信方式需要大量软件加密算法来进行信息安全保护不同。这是由于所传递的信息被分散在远场方向图的不同角度上，接收端只有同时并完整地获取了指定采样点上的数据，才能恢复出所发送的数据，而如果缺失其中某一点的远场信息，将无法还原原始信息。然而，对于星地传输这样的应用场景，由于各个采样点的间距往往达到几百甚至上千公里，而整个采样点的跨度更是超过上万公里，窃听者是无法在技术上做到同时获取这些采样点的信号，即使假设窃听者可以获取整个远场方向图，由于他并不知道当前的信道状态，即哪几个采样点被正在使用，以及这些采样点的数据(硬件 码)与原始发送信息(信息码)之间的映射关系，所以窃听者仍然无法复原原始发送的信息。这类似于现代数字通信系统中的跳频技术(FH)，即所发送的信号快速地在多个不同频率之间来回跳转，而由伪随机序列所决定的跳转频率点只有发射和接收双方所知。不同于跳频技术，直接辐射无线数字通信系统中所采用的实时估计信道的方式并不消耗额外的带宽。这一独特的性质意味着该通信系统是一种与生俱来的保密通信系统；直接辐射无线通信系统另一个优点是数字信号直接编码到可编程超材料上面，并且通过其直接辐射到自由空间，省去了传统通信系统之中加载中频载波的过程，大大简化了通信系统的复杂度。其次，本发明之中还编写了信道检测及信道优化的算法，可以使所提出的系统在不同的环境之中或者在受到干扰的情况下，迅速做出反应，进而检测出可用的编码状态，有效地保障通信速率及通信质量。
需要说明的是，以上所述仅是本发明的优选实施方式，由于本发明独有的利用远场方向图直接表征信息的方式，具有易于实现并且模仿的特点。应当指出：对于本技术领域的普通技术人员来说，在不脱离本发明原理的前提下，还可以做出若干改进和润饰，这些改进和润饰也应视为本发明的保护范围。

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  1. 基于数字编码超材料的直接辐射无线数字通信系统，包括发射系统和接收系统，其特征在于：所述发射系统包括控制模块、可编程超材料阵列和馈源天线，所述控制模块与可编程超材料控制线相连，用于将所需传递的信息转换为二进制码，加载在可编程超材料相应的控制线上；可编程超材料阵列包含若干可编程超材料单元，用于加载所述二进制码，在馈源天线的照射下这些携带有信息的二进制编码以不断变换的远场方向图的形式直接地辐射到自由空间；所述接收系统包括接收处理模块以及与接收处理模块具有信号连接的若干接收机，接收系统用于将处于远场区不同位置处的接收天线接收到的电场值汇总得到远场方向图，并通过远场方向图与编码序列之间的映射关系恢复出所发送的原始信息。
  2. 根据权利要求1所述的基于数字编码超材料的直接辐射无线数字通信系统，其特征在于：所述可编程超材料单元从上至下包括上层金属结构、F4B介质层和金属背板，上层的金属结构包括H形金属图案，所述H形金属图案中设置有二极管，所述二极管与H形金属图案具有电连接。
  3. 根据权利要求3所述的基于数字编码超材料的直接辐射无线数字通信系统，其特征在于：所述二极管采用具有开关状态的开关二极管或具有参数连续变化的偏压二极管。
  4. 根据权利要求1所述的基于数字编码超材料的直接辐射无线数字通信系统，其特征在于：所述接收机包括分布在不同角度的整流天线， 接收处理模块包括AD模数转换以及现场可编程门阵列FPGA处理系统。
  5. 基于数字编码超材料的直接辐射无线数字通信方法，其特征在于，包括如下步骤：
    将携带有原始信息的二进制编码将以不断变换的远场方向图的形式传递到远场区；
    将处于远场区不同位置处的接收天线接收到的电场值汇总得到远场方向图，并通过远场方向图与编码序列之间的映射关系恢复出所发送的原始信息。
  6. 根据权利要求7所述的基于数字编码超材料的直接辐射无线数字通信方法，其特征在于，在传递二进制编码之前还包括：
    将所需传递的信息转换为二进制码，加载在可编程超材料相应的控制线上。
  7. 根据权利要求7或8所述的基于数字编码超材料的直接辐射无线数字通信方法，其特征在于，还包括通信评估过程，所述通信评估过程包括：
    首先对一个具有N个控制列的可编程超表面所有的可能状态进行编码；
    然后对这2 N个不同的编码对应的远场方向图在M个不同的角度上进行采样，得到的数据存储在一个2 N行M列的矩阵A中；
    随后计算矩阵A各个行向量之间的欧氏距离D，之后将矩阵D下三角化，并将所有小于噪声门限的元素置0，其他元素置1，形成新的矩 阵D’，最后寻找D’中不含0元素的行标号，并输出到矩阵K中，即得到最终得到的可用状态的编码。
  8. 根据权利要求7所述的基于数字编码超材料的直接辐射无线数字通信方法，其特征在于，在通信评估过程之后还包括通信优化过程，所述通信优化过程包括：
    首先将不同角度采集到的远场方向图矩阵数据进行求解欧氏距离，得到欧氏距离矩阵D，将矩阵D中所有大于零的元素所在的行和列输出到i和j，将矩阵D中所有包含非零元素的行存储对应的行存储到矩阵b中，接下来判断b是否属于可用状态K，如果是则继续找下一行，如果不是则将b添加到可用状态K中，直至循环结束得到的K矩阵即包括经信道优化算法优化之后的所有可用状态。
  9. 基于数字编码超材料的直接辐射无线数字通信评估方法，基于数字编码超材料的直接辐射无线数字通信系统实现，其特征在于，包括如下步骤：
    首先对一个具有N个控制列的可编程超表面所有的可能状态进行编码；
    然后对着2 N个不同的编码对应的远场方向图在M个不同的角度上进行采样，得到的数据存储在一个2 N行M列的矩阵A中；
    随后计算矩阵A各个行向量之间的欧氏距离D，之后将矩阵D下三角化，并将所有小于噪声门限的元素置0，其他元素置1，形成新的矩阵D’，最后寻找D’中不含0元素的行标号，并输出到矩阵K中，即得到最终得到的可用状态的编码。
  10. 基于数字编码超材料的直接辐射无线数字通信优化方法，基于数字编码超材料的直接辐射无线数字通信系统实现，其特征在于，包括如下步骤：
    首先将不同角度采集到的远场方向图矩阵数据进行求解欧氏距离，得到欧氏距离矩阵D，将矩阵D中所有大于零的元素所在的行和列输出到i和j，将矩阵D中所有包含非零元素的行存储对应的行存储到矩阵b中，接下来判断b是否属于可用状态K，如果是则继续找下一行，如果不是则将b添加到可用状态K中，直至循环结束得到的K矩阵即包括经信道优化算法优化之后的所有可用状态。
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