The semi-physical simulation test method is a research hotspot of current electronic warfare weapon equipment performance evaluation test in complex electromagnetic environment. The complex electromagnetic environment signal generation technology based on digital geographic information is an effective technical way to realize semi-physical simulation test. This paper introduces the ideas, methods and development status of this technology from three aspects: complex electromagnetic environment simulation modeling, electromagnetic information propagation simulation based on digital geographic information and complex pattern signal generation.
1 Introduction
Electronic warfare is an important part of modern warfare. In many cases, the performance indicators of electronic warfare equipment directly determine the overall victory and defeat of war. However, the electromagnetic environment of the actual theater in which electronic warfare equipment is located is filled with a wide variety of complex electromagnetic signals, such as radar, navigation, communications, enemy interference, and natural noise. At the same time, because the propagation of various electromagnetic signals is significantly affected by the actual geographical environment, the electromagnetic environment in the theater is extremely complicated. The performance test of electronic warfare weapons and equipment in complex electromagnetic environment has become an important part of its development process [1].
In summary, the electromagnetic performance tests of weapons and equipment can be divided into three categories according to different environments. The first is the all-physical test, which places the equipment to be tested in a drill or actual theater, and tests the equipment performance using the actual complex electromagnetic environment. This method is the most convincing and is often used as the final test method for mature weaponry. However, because this method is extremely costly and risky, many occasions are destructive tests, and the test results obtained are not ergodic and cannot meet the vast majority of routine testing requirements in the equipment development process. The second is a full digital simulation test based on technologies such as computers and databases. This technology uses data acquisition or mathematical modeling to store the main characteristic information of the actual electromagnetic environment in a digital format in a database. Under the driving of a specific simulation algorithm, the performance of the equipment to be tested is fully digitally simulated. . This method is low in cost, flexible and convenient, and is usually used in the early development of equipment, and is biased towards testing software algorithms. However, due to the low fidelity and the excessive difference from the actual environment, the performance test of the formal equipment has only a reference function, and most of the occasions cannot be used as the final verification means. The third test method is a semi-physical simulation test, which is based on the organic combination of the first two methods. It uses data acquisition or mathematical modeling methods to build a digital complex electromagnetic environment information database, calculate waveform data according to the actual test scenario requirements, based on complex signal generation technology, generate actual electromagnetic signals by means of waveform generation, artificially construct high fidelity Complex electromagnetic environment for equipment performance testing. This test method combines the advantages of the first two methods. The test is efficient and convenient, breaking the time and space constraints of the test environment in the whole physical test; the scene is rich, and the test electromagnetic environment signal is arbitrarily constructed according to the actual needs of the actual environment; high fidelity, based on digital map data Comprehensive consideration of various factors such as radiation source type, equipment layout, transmission route, natural interference, low cost, comprehensive results, non-destructive testing, and highly consistent repeatability testing, which can be evaluated under various extreme conditions. performance.
The complex electromagnetic environment signal generation technology based on digital geographic information is an effective technical way to realize semi-physical simulation test. It has fast and convenient scene construction, remote controllable test, multi-parameter controllable interference signal, and high-efficiency test effect of interference effect evaluation. advantage. The technical problems are mainly reflected in three aspects: 1) Complex electromagnetic environment simulation modeling, the actual battlefield electromagnetic environment is extremely complex, including radar, communication, navigation, interference, noise and other complex style signals; the transmission medium is variable Covering the surface of the sea, the atmosphere, scatterers, etc.; the mobile and transmitter layout of the transmitter and receiver, the topology features are complex. 2) Simulation of electromagnetic signal propagation based on digital geographic information. Different geographical environments, such as fresh water, sea water, wetlands, forests and buildings, have attenuation effects such as diffraction, reflection and obstruction on the propagation of electromagnetic waves. Moreover, depending on the characteristics of the specific environment (such as the difference in salt content of seawater), the electrical properties of each type of geographical environment are different, resulting in complex changes in the parameters of the propagation model. 3) Complex pattern signal generation technology, the signal pattern is complex and variable in the actual complex electromagnetic environment, and the frequency coverage is large, covering the microwave millimeter wave frequency band, the modulation bandwidth is up to GHz, and has the agile frequency characteristic. Therefore, the complex pattern signal generation technology that satisfies the above requirements of performance indicators is to realize the simulation of complex electromagnetic environment signals and meet the basics of semi-physical simulation test.
This paper will introduce the ideas, methods and development status of complex electromagnetic environment signal generation technology based on digital geographic information from the above three aspects.
2. Complex electromagnetic environment simulation modeling
According to the definition given by the National Military Standard (GJB6130-2007), the complex electromagnetic environment means that a variety of electromagnetic signals exist simultaneously in a certain airspace, time domain, frequency domain and power domain, and the use of frequency equipment and combat operations are generated. The electromagnetic environment must be affected. It can be seen that the complex electromagnetic environment is a general term for various complex electromagnetic signal components contained in a certain actual scene. It is mainly composed of electronic countermeasures against the environment, radar environment, communication environment, photoelectric environment, enemy and electromagnetic environment, navigation electromagnetic environment, Civil electromagnetic environment, natural electromagnetic environment, etc. [2]. Each type of electromagnetic environment is generated by different types of electromagnetic radiation sources, and has an impact on different information weaponry, which in turn affects the overall operations. The premise of modeling complex electromagnetic environment is to classify and analyze the complex and complex signal components in a scene, and then model according to the characterization and propagation medium of each conventional signal [3]. Finally, the signals of interest will be integrated to complete the simulation of the actual electromagnetic environment.
2.1 Signal characteristics of complex electromagnetic environment
The signal components contained in the complex electromagnetic environment are mainly divided into two categories: natural factor interference signals and human factors interference signals. The human factor interference signals include unintentional interference signals and anti-interference signals. Natural factors Interfering signals are mainly caused by lightning and static electricity, and are uncontrollable factors in the actual environment. The construction of the electromagnetic environment for semi-physical simulation testing focuses on the simulation of interference signals with human factors with controllable characteristics. Because the anti-interference signal has a significant impact on the electronic weapon equipment, the form is diverse and the style is complex, which becomes the key content of the complex electromagnetic environment simulation. With the rapid development and upgrading of electronic warfare equipment, the electromagnetic signals used mainly exhibit the following four characteristics: 1) The signal patterns are complex and diverse, with many types and large distribution densities. The development of digital vector modulation technology has made the realization of a series of complex modulation patterns a reality. The modulation formats used in various new system radar equipments that are widely distributed in theaters cover linear modulation, nonlinear frequency modulation, phase coding, frequency coding, noise modulation, Barker code modulation and other intrapulse modulation formats, as well as inter-pulse frequency agility. , pulse group frequency agility, time-sharing frequency diversity, PRI staggered / jitter / group change / slip, pulse width group change / combination and other inter-pulse modulation formats. 2) The signal frequency coverage is greatly expanded. The frequency band occupied by the electromagnetic signals used in electronic equipment is constantly widening, covering from high frequency signals to microwave millimeter wave signals. 3) The signal modulation bandwidth is constantly increasing. For example, the modulation bandwidth of the new synthetic aperture radar reaches the order of GHz. 4) The frequency conversion performance is significantly improved and the signals are highly overlapping. The center frequency of the modulated signal used by some signal radars is up to the order of hundred nanoseconds, and millions of frequency agility can be achieved in one second. There may be millions of orders at the same time for conventional receivers. The signals appear at the same time and the overlap is severe.
It can be seen that the complex electromagnetic environment has a significant impact on the normal operation of electronic equipment, and poses great challenges to its operational use and performance. The realistic simulation construction of complex electromagnetic environment is the basis of semi-physical simulation test. It provides convenience for equipment to carry out complex electromagnetic environment test, study electromagnetic compatibility of weapon equipment, and detect its electromagnetic environment adaptability, which is beneficial to improve the electromagnetic environment of weapon equipment. Adaptability is of great significance.
2.2 Signal modeling of complex electromagnetic environment
According to the degree of influence of various radiation sources on electronic weapon equipment, the simulation of complex electromagnetic environment in theaters is mainly for the modeling of the following types of radiation sources, including pulse radar, jammer, TACAN, IFF, and joint. Tactical Information Distribution System (JTIDS), etc. [4]. The basic content of characterization of radiation sources can be summarized as follows: 1) general information, including identification, model, use, system, antenna type, horizontal coverage, vertical coverage, reconnaissance distance, maximum tracking distance, integrated loss, number of beams , maximum beam number, minimum scan step, maximum gain power, platform type during scanning, platform performance, command and control relationship, signal pattern, etc.; 2) transmitter information, including model, operating frequency band, bandwidth, feeder loss, transmitter Type, etc.; 3) Receiver information, including model, sensitivity, center frequency, bandwidth, IF bandwidth, etc.
In modeling the source signal, the pulse descriptor (PDW) is usually used to describe the radiation information of the radiation source, including: pulse carrier frequency, pulse width, intrapulse modulation (phase encoding or frequency modulation), pulse arrival time, Pulse arrival angle, pulse amplitude. The radar signal received by the receiver in the electronic warfare environment is a superposition of the pulse streams radiated by the respective radiation sources. The pulse streams received by the receiver are ordered by the time the pulses arrive at the receiver. The radiation source pulse stream is the basic element of the receiver pulse stream. The complexity of the radiation source pulse stream and the variation of the pulse parameters determines the complexity of the scene. According to the possible variations of the radiation source pulse flow and the targeted processing methods, the radiation source pulse flow can be modeled from several aspects such as time domain, spatial domain and modulation domain.
(1) Time domain model
Pulse arrival time (TOA) is one of the most important parameters of the pulse flow. The TOA is related to the distance between the radiation source and the receiver and the pulse repetition interval (PRI) of the radiation source. The PRI is different for different types of radiation sources.
(2) Airspace model
The pulse arrival angle (DOA) is a closely related information to the location of the source, depending on the relative angle between the source and the receiver. When there is relative motion between the radiation source and the receiver, the DOA is slowly changing. The DOA parameters are not affected by the radiation source itself and are the most important and reliable features on which the signal processing system is based. Therefore, it is necessary to model and analyze the DOA separately.
(3) Modulation domain model
The modulation domain parameters mainly include: pulse carrier frequency (RF), pulse width (PW), pulse amplitude (PA), and intrapulse modulation pattern (PM). The parameter domain parameters are different for different types of radiation sources.
According to the radiation source parameters set in the war file, the PDW flow generated by each radiation source during the current simulation time interval is generated, and the signal is diluted according to the state parameters of the passive radar for each simulation time, and finally the PDW flow of all the radiation sources is performed. Sort the output.
3. Simulation of electromagnetic signal propagation based on digital geographic information
Starting from the needs of electromagnetic environment simulation, whether it is natural factors interference signals and human factors interference signals, to fully simulate the physical basis of the electromagnetic environment, it is necessary to decompose the physical environment that affects the generation and propagation of the electromagnetic environment in detail, and establish a basic The simulated object, that is, the geographic information of the battlefield physical environment, such as terrain, meteorology, geology, geomagnetism and other factors. According to the different frequency coverage of electromagnetic signals emitted by different radiation sources in a complex electromagnetic environment, the propagation modes of signals vary. For example: 1) Surface wave propagation refers to the propagation of radio waves along the surface of the Earth. At this time, the radio waves are transmitted close to the ground, and the nature, geomorphology, and features of the ground affect the propagation of radio waves. 2) Sky wave propagation refers to the propagation of radio waves that are reflected by the ionosphere to the ground. The ionosphere is composed of four conductive layers at different heights around the earth. These four conductive layers are called D layer, E layer, F1 layer and F2 layer, respectively. These conductive layers have an important influence on short wave propagation. 3) Space wave propagation refers to the propagation of electromagnetic waves directly from the transmitting antenna to the receiving antenna in the line of sight when the transmitting and receiving antennas are erected. At this time, the electromagnetic wave can also be reflected by the ground to reach the receiving antenna. Therefore, the field strength at the receiving antenna is the vector sum of the direct wave and the reflected wave, and the combined field strength is formed. The direct wave is not affected by the ground, and the ground reflected wave passes through. The reflection of the ground is therefore affected by the geological topography of the reflection point. 4) Outer space propagation refers to the propagation of electromagnetic waves from the ground, through the low-altitude atmosphere and ionosphere to the outer space and the propagation of the opposite process. 5) Scattering propagation refers to the presence of irregular airflow in the troposphere of the atmosphere, in addition to regular flaky or laminar airflow, which is similar to the unequal body of vortices in the water stream. Accordingly, there is unevenness in electron density in the ionosphere. When radio waves are projected onto these inhomogeneities, similar to the scattering and reflection phenomena of light, the waves will be scattered or reflected, and some of the energy will be transmitted to the receiving point. This mode of propagation is called scatter propagation. 6) Atmospheric waveguide propagation refers to the formation of an atmospheric waveguide for a specific frequency under certain conditions due to the heterogeneity of the troposphere in the atmosphere and the existence of the ionosphere, so that the loss of radio wave propagation is greatly reduced. The phenomenon is called atmospheric waveguide propagation. According to the signal components of the actual battlefield electromagnetic environment, the signal propagation modes of electronic warfare equipment are mainly surface wave propagation and spatial wave propagation, which are significantly affected by the actual geographical environment. Geographic Information System (GIS) is an effective tool to realize simulation modeling of electromagnetic signal propagation based on geographic information.
The GIS system is a technical system that collects, stores, manages, calculates, analyzes, displays and describes geographically distributed data in whole or part of the Earth's surface space with the support of software and hardware [5]. The objects processed and managed by the GIS system are a variety of geospatial actual data and their relationships, including spatial positioning data, graphic data, remote sensing image data, attribute data, etc., for analyzing and processing various phenomena and processes of a certain geographical area distribution. The GIS system includes three types of spatial data: 1) coordinate systems such as latitude and longitude, plane rectangular coordinates, and polar coordinates. 2) Topological structure, defining the relationship between the connection and the adjacency between two objects. 3) Geographical variables such as soil type, geological information, climate, etc. At the same time, the GIS system supports two kinds of data structures. 1) The raster data structure, that is, the pixel array, can determine the position according to the unique column number of each pixel. Each code in the raster data structure explicitly represents the attributes of the corresponding entity. It consists of a level 3 mechanism, that is, a point entity, which represents a pixel in the raster data; a line entity, which represents a set of adjacent cells in a certain direction; and a face entity, which represents adjacent cells that are clustered together. set. 2) Vector data structure, that is, by recording the coordinates, the point, line, and surface geographic entities are accurately reflected as much as possible. It has higher accuracy than raster data. Vector data can be converted to raster data according to a certain conversion law. The structural characteristics of the raster data are beneficial to computer processing, and have the analysis functions of distance mapping, density mapping, surface generation and analysis, unit statistics, domain statistics, classification area statistics, reclassification and grid calculation.
Based on the raster data of the GIS system, the topographic map of the battlefield area and the distribution map of the required electromagnetic radiation source are established through the acquisition and vectorization of the graphics. The database is used to establish the basic geographic information database of the electromagnetic radiation source, through the electronic map and database. The connection, creation and query of information on the characteristics, attributes, spatial location, detection capabilities and communication capabilities of the battlefield electromagnetic radiation source. Simultaneously realize the visualization of the number of radiation sources, spatial distribution, technical and tactical indicators, tactical applications, organizational sequences and electromagnetic signal propagation paths, electromagnetic radiation range, electromagnetic spectrum distribution and other content, providing simulation modeling for complex environments based on the actual geographical environment of the battlefield. stand by.
4. Complex pattern signal generation technology
The complex pattern signal generation technology is to finally realize the complex and variable electromagnetic signal in the complex electromagnetic environment, artificially construct a complex electromagnetic environment with high fidelity, and adapt to the performance test of various equipments. The ideal complex pattern signal generation technology is an organic combination of a complex style simulation software system based on a digital complex electromagnetic environment information database and a complex style signal generation simulation hardware platform. The advantages of this technology are as follows: 1) A platform can be equipped according to different weapons and equipment. Test requirements, equipped with a complex complex electromagnetic environment information database and simulation generation software to achieve radiation source and its environment simulation in accordance with the weapon equipment combat environment; 2) a generation of platforms can be equipped with multiple generations of complex electromagnetic environment simulation software of the same weapon equipment, It has strong analog simulation compatibility and applicability. This complex-style signal generation technology can be used to test multiple, multi-generation weapons and equipment through flexible configuration, improve test performance, get rid of the time domain, airspace and geographical limits of the whole physical test environment, and satisfy weapons on a unified platform. Equipment testing requirements for environmental simulation styles, spectrum coverage, modulation bandwidth, and signal agility.
The key technical point in the simulation software system based on the complex electromagnetic environment information database is to adapt to various equipments and include the database and model establishment that conform to the geographic information of the equipment combat area. This has been highlighted in the previous article and will not be described again. For the key indicators of complex pattern signal generation technology that rely on the hardware platform, the technical indicators involved are extensive, and the performance indicators are very high. For example, the frequency coverage is large, covering the microwave millimeter wave frequency band, and the modulation bandwidth is up to GHz. At the same time, it has a frequency conversion feature. The complex pattern signal that can support the above high-performance technical indicators is inseparable from the support of the high-performance signal generation hardware platform. At present, the signal generation hardware platform is used to realize the electromagnetic signal generation in the complex electromagnetic environment. The key technical points that need to be solved are as follows: 1) The large bandwidth arbitrary wave baseband generation technology is to realize the complex electromagnetic environment information data from the data volume to the simulation. The core unit of the quantity conversion has a wide modulation bandwidth and forms a modulated complex intermediate frequency analog signal through digital-to-analog conversion. The analog signal will be moved to the required frequency band by the corresponding frequency synthesis technology to realize the final output of the complex pattern signal; 2) The digital signal synthesis technology of the complex pattern signal multi-parameter multi-domain modulation integrated simulation will be in the complex electromagnetic environment information database. The data is comprehensively calculated and processed in the form of numbers, and the superposition of the required signals in the frequency domain, the time domain, the modulation domain, and the spatial domain is completed, and finally, the editing, definition, and definition of complex electromagnetic signals of large-capacity, multi-pattern, and multi-modulation parameters are realized. Data storage, invocation and other tasks, finally complete the carrier and sequence group construction of complex electromagnetic signal simulation, ready for the outward generation of complex pattern signals; 3) frequency synthesis technology that covers microwave millimeter waves and can support complex pattern signal generation, The direct analog frequency synthesis (ADS) method (such as microwave millimeter wave frequency signal generator) or indirect frequency synthesis (such as vector signal generator) is used to realize the modulated complex pattern carrier signal to a higher frequency band.
5 Conclusion
Complex environmental signal simulation technology based on digital geographic information is a new attempt of semi-physical simulation test of electronic weapon equipment. The performance evaluation test system of weapon equipment based on this technology in complex electromagnetic environment has the advantages of convenient operation, controllable parameters, low cost, high fidelity, comprehensive results and rich scenes. This paper introduces the ideas, methods and development status of this technology from three aspects: complex electromagnetic environment simulation modeling, electromagnetic information propagation simulation based on digital geographic information and complex pattern signal generation. The feasibility of this technology is analyzed in detail.
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