Measurement and control system simulation and measurement and control equipment software technology

I. Overview
　　The 21st century is the century of space exploration and the century of scrambling for space domination. The operation of aircraft and missiles cannot be separated from the support of measurement and control systems. In the past, the functions and equipment flexibility of measurement and control systems were relatively poor. Once the system and equipment were installed, it was difficult to adapt to the launch, tracking and orbit determination and management tasks of new or other types of satellites. Therefore, modularization and standardization of measurement and control equipment are the inevitable trend of the development of new measurement and control technologies. The development of the aerospace industry has put forward new requirements for measurement and control equipment, which requires cost reduction and shortening of development cycles. To this end, through computer simulation of measurement and control equipment and the extensive use of computer software or advanced intelligent software, the hardware structure is simplified, which can effectively reduce costs, improve system reliability and shorten the equipment development cycle. In addition, the integration and digitization of measurement and control equipment has become the development direction of electronic system engineering, and is also a new technology that must be adopted in the development of measurement and control communication technology. Digitization is the basis for the softwareization of measurement and control equipment. Computer simulation provides an important technical means for the modularization, standardization and optimization design of equipment reconfiguration solutions.

II. Equipment-level simulation technology for measurement and control systems
1. Background of the demand for measurement and control equipment simulation technology
　　At present, the high cost of missile weapon systems and aerospace engineering has become a crucial constraint on the development of aviation, aerospace and national defense forces in various countries. System development, training and exercises in have become a way out for the military of various countries to get out of the predicament. As a strategic technology, system simulation technology is of great importance in the development of measurement and control systems.
　　In the process of measurement and control system development, the establishment of a new system measurement and control system must be rigorously demonstrated. Through system simulation, the measurement and control systems of different systems can be verified and optimized from the overall design, and their feasibility and related technical indicators and performance can be predicted and evaluated, so as to improve the quality and efficiency of the design, analysis and test verification of missile weapon and spacecraft measurement and control systems, and shorten the development cycle. Measurement and control system simulation is divided into system-level and equipment-level simulation. System-level simulation is to jointly design satellites and ground stations to determine the constellation form, communication mode, orbit determination method, satellite-ground indicators, etc. Equipment-level simulation needs to ensure the accuracy of the orbit measurement of the aircraft and the accuracy of the instructions and data transmission, and propose reasonable extension indicators, focusing on the impact of the measurement and control system, various signal forms, modulation and demodulation system, combined interference, short stability of the signal, group delay of the channel, error correction coding/decoding, etc. on the accuracy of ranging and speed measurement and the impact on the bit error rate of digital transmission. Through the construction of the equipment-level integrated simulation platform of the measurement and control system and the simulation operation of the simulation scheme, the equipment-level scheme design and indicator allocation can be optimized, so that the actual developed system can get rid of the previous reliance on repeated actual tests and use experience to guide the design of the equipment-level system, thereby improving the quality and efficiency of the equipment-level design and analysis of the measurement and control system, and improving the accuracy of the aircraft's orbit measurement and data transmission under the condition of optimizing resource allocation.
2. Overview of domestic and foreign development
　　In advanced countries, simulation has long become a tool, widely used in the full life cycle activities of various systems and personnel training decision-making processes.
　　In the field of measurement and control, the construction of a new measurement and control system in advanced countries such as the United States is currently designed from top to bottom through system simulation technology. The top-level design includes station distribution, system measurement and control system, frequency arrangement, and expected orbit accuracy. Through simulation, analysis and optimization are performed to propose satellite and ground equipment indicators. The equipment development department conducts equipment-level system design based on the indicators proposed by the large system. First, the module function is determined, and then the hardware description language (VHDL) or DSP C or assembly code is generated from the algorithm of the functional module. Then, logic synthesis is performed to generate gate-level netlists, and finally, board-level circuit products such as FPGA, ASIC, and DSP of the target system are formed. In this top-down simulation design process, the next-level module can often be embedded in the upper-level environment for joint simulation, and the design can be continuously modified and improved so that the final target system can fully meet the system requirements. Therefore, the overall measurement and control technology, measurement and control networking technology, simulation, equipment simulation design, and software radio reconfigurable technology have formed a top-down unity, bringing a new concept to the construction of aerospace measurement and control systems.
　　In China, the current development of measurement and control systems basically involves system design first and then circuit design. System design is mainly based on theoretical analysis and past successful experience. When designing a new system, it is often necessary to refer to multiple different systems with the required functions, make reasonable improvements and integration, and allocate indicators to each subsystem or unit. The subsystem or unit is developed according to the function and indicator requirements, and finally the system is tested together, and the problems are improved. If major problems are found in the system design during the test, the design of each subsystem or unit must be changed. This development method is very likely to cause a waste of manpower, material resources, financial resources and time.
3. Technical characteristics of measurement and control system equipment-level simulation
　　Measurement and control system equipment-level simulation mainly uses computer software simulation technology, with the help of computers, to test the real system or the imagined system with the system model. Measurement and control system equipment-level computer software simulation has the following characteristics:
　　(1) The use of software simulation technology for testing can greatly reduce costs, especially for large-scale measurement and control communication systems, which can reduce expensive hardware investment. At the same time, the simulation equipment can be reused, and its test environment and test plan are very easy to change, which can shorten the test cycle;
　　(2) It is conducive to the rapid absorption of the continuously developing advanced measurement and control and communication technologies, and the continuous improvement of measurement and control or communication modules;
　　(3) It is easy to optimize the design. For the measurement, control and communication system in the scheme stage, the system model can be designed first, and simulation can be used for repeated tests to find the optimal system structure and parameters, so as to optimize the system design and improve the design level;
　　(4) It can be very close to the actual system, providing an accurate evaluation method for engineering design, avoiding the limitation of hardware simulation on the number of test equipment and the level of simulation devices;
　　(5) Through computer software simulation, it is convenient to accurately, quickly and conveniently process simulation results and data, and it is conducive to data preservation and post-analysis.
4. The main task of the measurement and control system equipment-level simulation
　　The main task of the measurement and control system equipment-level simulation is to conceptually model the real or imagined system, and to establish the mathematical model and simulation model for distance measurement and speed measurement accuracy analysis on the basis of the clear system model, and to establish the mathematical model and simulation model for telemetry, remote control, voice and data transmission bit error rate analysis. Through the operation of the simulation model, the simulation analysis of the system distance measurement, speed measurement accuracy index and bit error rate index is obtained, the system operation status is qualitatively analyzed from the functional principle, and the system operation status is quantitatively analyzed from the scheme and technical indicators, and the consistency with the actual measurement and control station system operation results is obtained.
　　On the other hand, in the design of subsystems and components, by establishing mathematical models of each subsystem and component in the ground equipment of the measurement and control system, simulating data flow, control flow and working status, analyzing the dynamic characteristics and steady-state characteristics of the system, and verifying and evaluating the overall and subsystem solutions. First, establish mathematical models of each subsystem and component. The mathematical model of each subsystem adopts a single module design, and the components inside each subsystem module also adopt functional module design. Each functional module is stored in the runtime library in the form of a library module. By selecting different functional modules, subsystems with different functions can be formed. Then, according to the data flow, control flow and working status of each subsystem, organize the independent simulation of the subsystem, and then simulate the whole system through the overall measurement and control communication plan. When the subsystem is simulated independently, the influence of other subsystems on it is taken as the external input of the subsystem, and the external environment simulation module is used to generate equivalent external input. From the subsystem to the overall simulation, the principle of combination should be met.
5. Development direction of measurement and control simulation technology
　　At present, system simulation technology has become a national key technology and national defense key technology that developed countries focus on developing. The rapid development of information technology in the 21st century will enable simulation technology and aerospace technology to be closely integrated at all levels.
　　Measurement and control system simulation technology can provide optimization solutions and key technology designs for future space-based measurement and control, small satellite measurement and control, deep space measurement and control and other systems. In the field of aerospace simulation, we will focus on the development of constellation simulation technology to achieve distributed interactive simulation of satellite in-orbit operation and multi-satellite management. Through the participation of the satellite itself and the ground station, each satellite can coordinate operation and maintain accurate position and attitude and working status connection. For various satellite systems from development to operation, system models and simulation systems including ground application systems and satellites should be established according to the situation in order to analyze, optimize and support the long-term operation of satellites and training of management personnel.

3. Software technology of measurement and control equipment
1. New features of the development of measurement and control equipment technology
　　The aerospace measurement and control system is a complex system, which involves different modulation systems, working modes, information transmission and data modulation and demodulation processing. In the past, China's satellite measurement and control station construction model was basically that a new measurement and control station had to be developed for each satellite (the main new development content was reflected in the terminal equipment). In order to meet the requirements of different measurement and control tasks, the equipment was often huge and it was necessary to repeatedly build hardware equipment with similar functions. With the rapid development of computer technology and digital signal processing technology, measurement and control equipment has gradually developed in the direction of integration, digitization, modularization and standardization. By adopting high-speed A/D, DSP, FP-GA, MPU, DDS, digital-analog hybrid integrated circuits, high-speed large-capacity storage computers and network technology, bus technology, high-speed digital signal processing and data processing are completed, and speed measurement, distance measurement, telemetry, remote control, data transmission and monitoring are integrated into one, and integrated and integrated design is carried out. The main contents of modularization and standardization of measurement and control equipment include unit modularization, function, technical indicator serialization, interface standardization and normalization.
　　The new features of the development of measurement and control equipment technology have promoted the application of software radio technology in the field of measurement and control communication. Digitalization is the basis of the softwareization of measurement and control equipment, and softwareization is a good technical approach to achieve the integration, standardization and normalization of measurement and control equipment. [page]
2. Technical basis of softwareization of measurement and control equipment
　　The technical theory of softwareization of measurement and control equipment is software radio. Software radio technology breaks through the design limitations of traditional radio equipment with single-function and poor scalability hardware as the core, emphasizes the new design idea of ​​using open and simple hardware as a universal platform and using programmable, upgradeable and reconfigurable application software to realize various radio functions as much as possible. Users can choose different application software to meet the needs of different functions in different periods and different use environments on a universal and scalable hardware platform, and can adapt to the continuous development of technological progress, save a lot of hardware investment, greatly shorten the research and development cycle of new products, and adapt to market changes in a timely manner. The
　　basis of softwareization of measurement and control equipment is digitalization, and its core is the ultra-high-speed time response and ultra-large-scale high integration of digital devices and chips. At present, microelectronics technology is developing rapidly. The number of transistors on a single integrated chip doubles every 18 months. In 2001, an integrated chip with 1 billion transistors was launched. In the next 20 years, an integrated chip with 1 trillion transistors will appear. The high degree of integration of digital circuits provides a strong guarantee for the development of software technology for measurement and control equipment.
3. Characteristics of software technology for measurement and control equipment
　　Software technology for measurement and control equipment is to use programmable technology to load different software to achieve multiple uses of one machine and one station, thereby completing measurement and control tasks with multiple functions and multiple technical states. The main technical features of software-based measurement and control equipment are:
　　(1) Software-based is highly flexible. By adding software modules, new functions can be easily added. Software modules can be changed or updated through wireless loading, and the software modules can be selected according to the strength of the required functions.
　　(2) Software-based is highly open. It adopts a modular and standardized structure. The hardware can be updated or expanded with the development of devices and technologies, and the software can be continuously upgraded as needed.
　　(3) Software-based can easily apply a variety of software algorithms for data smoothing, system error correction, modeling and predictive analysis, linear or nonlinear compensation, and fuzzy control under specific conditions, thereby effectively improving measurement and control accuracy.
　　(4) Software-based can greatly reduce the types and quantities of equipment hardware, improve the level of equipment miniaturization and system reliability, and greatly reduce the research and development costs of the measurement and control system.
    (5) Software-based is convenient for modularization and standardization of measurement and control equipment.
4. Contents of software technology for measurement and control equipment
    Software technology for measurement and control equipment mainly includes:
　　(1) Measurement and control video data processing software technology, including data processing module, reconfigurable monitoring software module, post-data processing module, etc.;
　　(2) Modularization and reconfiguration technology of channels and software extension from intermediate frequency to radio frequency;
　　(3) Programmable, reconfigurable, modular and standardized technology for terminal equipment;
    (4) Antenna pointing programming control technology.
5. Development direction of software technology
　　Software technology for measurement and control equipment is dominated by software. All its working processes and parameter processing can be defined and controlled by software. Its development direction can be explained from the following aspects:
　　(1) RF front-end sampling digitization technology. The purpose of software radio is to simplify the RF analog front end as much as possible, so that the A/D conversion is as close as possible to the antenna to complete the digitization of the analog signal, and the digitized signal should be processed by software as much as possible to achieve various functions and indicators. With the rapid increase in the frequency response rate of digital chips and devices, the rate of several gigahertz has reached the stage of engineering application. It can be imagined that in the near future, there will be a major breakthrough in the digitization of RF direct bandpass sampling;
　　(2) Baseband space transmission. In wireless transmission, the sine wave with strict regular characteristics has always been the main form of carrier signal. Baseband space transmission is to abandon the sine wave carrier modulation and directly realize space transmission in digital form. Its propagation medium is a very narrow time domain pulse with a pulse width of generally less than 1 ns. Its signal energy is distributed in the range from direct current (DC) to several gigahertz, and can be radiated and received with low distortion by ultra-wideband antennas;
　　(3) Software testing and identification technology. Since software plays a leading role in software-based measurement and control equipment, the correctness and reliability testing and identification of software will become a specialized technology.

4. Comprehensive application of measurement and control system simulation and measurement and control equipment software technology
　　At present, several popular communication simulation design platforms such as COSSAP, SPW, SystemView, etc. can meet the design and simulation requirements at different levels, from digital signal processing, filter design to complex communication systems. In these systems, complex analog, digital, hybrid and multi-rate systems can be constructed in DSP, communication and control systems. The system has a large number of optional libraries, allowing users to selectively add communication, logic, DSP and RF/analog functional modules, and can perform various system time domain/frequency domain analysis, and can perform theoretical analysis and distortion analysis on RF/analog and its hybrid systems. Of course, the simulation platform of the general communication system cannot meet the application simulation requirements of the measurement and control communication system to a large extent. The simulation of the measurement and control system on the general platform (the simulation platform can be developed independently) focuses on solving special problems in the measurement and control field. It not only has qualitative simulation analysis on the system principle, but more importantly, it needs to consider the performance of the actual components of the subsystem and component design indicators. Quantitative simulation analysis guides the actual design of the system and subsystem, and even directly generates practical code for DSP, FPGA or VHDL.
　　The simulation of the measurement and control system focuses on establishing an open simulation architecture that can adapt to the continuous development of technology and needs, and supports the construction of simulation systems in a combined manner. The simulation system consists of modular components with well-defined functions and standardized interfaces between components. At the same time, the simulation system consists of a general simulation support structure and an independent simulation application model. Each subsystem in the measurement and control system is composed of numerous functional components interconnected, such as encoders, modulators, sidetone generators, upconverters, demodulators, decoders, distance extractors, downconverters, frequency synthesizers, low-noise amplifiers, amplifiers, phase-locked loops and other hardware devices and data acquisition, packaging, display, storage, printing and other software units. The characteristics of its functional components often vary slightly with the parameters and technical requirements of the aircraft being measured and controlled. Therefore, they can be designed as standard modules, and users can select them appropriately according to mission requirements. When running joint simulations from components, subsystems to system levels, the algorithm of the functional module generates hardware description language (VHDL) or DSP C or assembly code, provided that the results meet the task requirements and expected indicators, and then performs logic synthesis to generate gate-level netlists, and finally forms board-level circuit products such as FPGA, ASIC, and DSP of the target system, realizing the softwareization of the measurement and control equipment functions.
　　Since softwareization is based on digitization, at the current level of device technology development, the current softwareization of measurement and control equipment is mainly reflected in the softwareization of measurement and control system terminals (i.e., baseband equipment below 70 MHz intermediate frequency). The softwareization of terminal equipment conveniently realizes the reconfiguration of terminal equipment. The requirements of this reconfigurable terminal for digital computing are mainly real-time and accuracy, including computing speed, computing power, data storage capacity, data throughput, etc. There are two ways to realize the softwareization of terminal equipment. One is to use DSP to implement it. With the emergence of new DSP devices, the amount of computing that DSP can provide has been greatly improved, and many algorithms implemented by ASIC may be gradually transferred to DSP implementation to achieve higher flexibility. However, at the current technical level, this solution has the disadvantages of high power consumption and slow processing speed. The second is to use DSP and FPGA to implement it. In the past, FPGA was used as a rapid prototyping method for ASIC design, which was an intermediate process. Now, using FPGA directly for system design can reduce the number of ASIC chips required, improve flexibility, and significantly shorten the development time. The benefit is that a single or relatively small number of chips can support more standard combinations.
　　Therefore, the components, subsystems and overall system solutions in the measurement and control system can be evaluated through simulation operation and analysis. Since the simulation module is modularized and standardized in function, the terminal module in the overall solution can realize the softwareization of the measurement and control equipment through a dedicated interface, closely combining system simulation with software technology to form a new model for the development of future measurement and control systems.

V. Conclusion
　　At present, in the development of measurement and control system equipment, there are only a few examples of special research using simulation technology, and there is still a long way to go before integrated and comprehensive simulation applications. Relatively speaking, the software technology of measurement and control equipment is more mature, but the efficiency in actual engineering applications is still not high, and we need to make a good summary. The organic combination of measurement and control system simulation technology and equipment software technology will be an important direction for us to focus on practical research for a long time in the future.

[1] Shi Shuji, Sun Jian, Liu Jiaxing. Aircraft Measurement and Control System [M]. Beijing: National Defense Industry Press, 1999.
[2] Sun Zhaowei, et al. Integrated System of Small Satellite Design, Analysis and Simulation Verification [J]. Journal of System Simulation, 2001 (5).
[3] Zhu Zhiqin. Current Status and Development of Vehicle Measurement and Control Software Technology [J]. Missiles and Space Launch Technology, 2002, (2).
[4] Wu Yi, et al. Communication System Software Simulation Technology [J]. Communications and Computers, 1999. (6).