Computer paper model 1: composition and application scenario analysis of cognitive radio system
Cognitive radio system composition
Cognitive radio system refers to a wireless communication system using cognitive radio technology, which makes the communication system more flexible with a more flexible transceiver platform and enhanced computing intelligence. Cognitive radio system mainly includes three functional modules: information acquisition, learning, decision-making and adjustment, as shown in figure 1 [3].
The main feature of cognitive radio system is to acquire the knowledge of radio external environment, internal state and related policies, as well as the ability to monitor users' needs. Cognitive radio system has the ability to acquire and analyze the external environment of radio. For example, by analyzing the current spectrum usage, we can display the carrier frequency and communication bandwidth of the wireless communication system, and even get its coverage and interference level. Cognitive radio system has the ability to obtain the internal state information of radio, which can be obtained through its configuration information, service load distribution information and transmission power. Cognitive radio system has the ability to obtain relevant policy information, which specifies the frequency band, maximum transmission power, frequency and bandwidth of adjacent nodes that cognitive radio system can use in a specific environment. Cognitive radio system has the ability to monitor users' needs and make decision adjustments according to users' needs. As shown in table 1, users' service requirements can generally be divided into three categories: voice, real-time data (such as images) and non-real-time data (such as large file packages), and different types of services have different requirements for communication QoS.
The second main feature of cognitive radio system is learning ability. The goal of the learning process is to improve the performance by using the decision and result information previously stored in the cognitive radio system. According to the different learning contents, learning methods can be divided into three categories. The first is supervised learning, which is used to learn the external environment, mainly using measurement information to train the estimator; The second is unsupervised learning, which is used to learn the external environment, mainly to extract the changing law of the relevant parameters of the external environment; The third category is reinforcement learning, which is used to learn internal rules or behaviors, mainly through the reward and punishment mechanism to highlight the rules or behaviors that are suitable for the current environment and abandon the rules or behaviors that are not suitable for the current environment. According to the learning mechanism, machine learning technology can be divided into mechanical learning, explanation-based learning, guided learning, analogy learning and inductive learning.
The third main feature of cognitive radio system is that it can dynamically and autonomously adjust its working parameters and protocols according to the acquired knowledge to achieve some predetermined goals, such as avoiding adverse interference to other radio systems. The adjustability of cognitive radio system does not require user intervention. It can adjust the working parameters in real time to achieve appropriate communication quality; Or changing the radio access technology in the connection; Or adjusting the radio resources in the system; Or adjust the transmission power to reduce interference. Cognitive radio system analyzes the acquired knowledge, makes decisions dynamically and autonomously, and reconstructs it. After making reconfiguration decisions, in response to control commands, the cognitive radio system can change its operating parameters and/or protocols according to these decisions. The decision-making process of cognitive radio system may include understanding the needs of multi-users and wireless working environment, and formulating strategies. The purpose of this strategy is to choose the appropriate configuration to support the same needs of these users.
Relationship between cognitive radio and other radios
Before cognitive radio was put forward, there were already some? A radio? Concepts such as software-defined radio and adaptive radio and their relationship with cognitive radio are shown in Figure 2. Software radio is considered as the enabling technology of cognitive radio system. Software-defined radio can work without the characteristics of CRS. SDR and CRS are in different stages of development, that is, the radio communication system using SDR has been used, while CRS is in the research stage, and its application is also under study and experiment. SDR and CRS are not radio communication services, but technologies that can be used comprehensively in any radio communication service. Adaptive radio can adapt to the preset channel and environment by adjusting parameters and protocols. Compared with cognitive radio, adaptive radio can't learn from the acquired knowledge and decision, and can't improve the way of knowledge acquisition and adjust the corresponding decision through learning, so it can't adapt to the preset channel and environment. Reconfigurable radio is a kind of radio that can change the hardware function through software control. It can update some or all physical layer waveforms and higher layers of the protocol stack. Policy-based radios can be updated to adapt to local regulatory policies without changing internal software. For newer radio networks, Internet routers are always policy-based. In this way, network operators can use policies to control access rights, allocate resources and modify network topology and behavior. For cognitive radio, policy-based technology should be able to make products universal, automatically adapt to local regulatory requirements, and automatically update regulatory rules when they change with time and experience. Smart radio is a kind of radio that predicts the future according to the past and present situation and makes adjustments in advance. Compared with smart radio, adaptive radio only determines the strategy and adjusts it according to the current situation, while cognitive radio can learn, determine the strategy and adjust it according to the previous results.
Key Technologies of Cognitive Radio
The key technologies of cognitive radio system include wireless spectrum sensing technology, intelligent resource management technology, adaptive transmission technology and cross-layer design technology, which are the characteristic technologies that distinguish cognitive radio from traditional radio [4,5].
Spectrum detection can be divided into physical layer detection, MAC layer detection and multi-user cooperative detection according to detection strategies, as shown in Figure 3. 3. 1. 1 Physical layer detection The physical layer detection method mainly determines whether the authorized frequency band is occupied by detecting whether there is an authorized user signal in time domain, frequency domain and space domain. Physical layer detection can be divided into the following three ways: the main methods of transmitter detection include energy detection, matched filtering detection and cyclostationary characteristic detection, and multi-antenna detection based on one of them. When the authorized user receiver receives the signal, the local oscillator must be used to convert the signal from high frequency to intermediate frequency. In this conversion process, the energy of some local oscillator signals will inevitably leak out through the antenna, so a low-power detection sensor can be placed near the authorized user receiver to detect the energy leakage of local oscillator signals, so as to judge whether the authorized user receiver is working. The interference temperature model makes people change the way of evaluating interference from the operation of a large number of transmitters to the real-time interaction between transmitters and receivers in an adaptive way. Its basis is the interference temperature mechanism, that is, by authorizing users to receive the interference temperature, the interference sources in the wireless communication environment can be quantitatively managed. MAC layer detection mainly focuses on how to improve throughput or spectrum utilization under multi-channel conditions. In addition, by optimizing the channel detection sequence and detection period, the number of available idle channels detected is maximized or the average search time of channels is minimized. MAC layer detection can be mainly divided into the following two ways: active detection is periodic detection, that is, when cognitive users have no communication needs, they will also periodically detect related channels, and the statistical characteristics of channel usage can be estimated by using the information obtained from periodic detection. Passive detection is also called on-demand detection. Cognitive users only detect all authorized channels in turn when they have communication needs until they find available free channels. Due to unfavorable factors such as multipath fading and shadow, it is difficult for a single cognitive user to make a correct judgment on whether there is an authorized user signal, and multiple cognitive users need to cooperate with each other to improve the sensitivity and accuracy of spectrum detection and shorten the detection time. Cooperative detection combines the detection technology of physical layer and MAC layer functions, which requires not only high-performance physical layer detection technology for each cognitive user, but also efficient scheduling and coordination mechanism for MAC layer.
The goal of intelligent resource management is to meet the QoS requirements of users, maximize the spectrum efficiency and system capacity on limited bandwidth, and effectively avoid network congestion. In cognitive radio system, the total capacity of the network is time-varying, so it is necessary to adopt certain access control algorithms to ensure that newly accessed connections will not affect the QoS requirements of existing connections in the network. Conceptual models of dynamic spectrum access can generally be divided into three categories, as shown in Figure 4. The dynamic dedicated mode retains the basic structure of the current static spectrum management policy, that is, the spectrum is authorized for specific communication services. The main idea of this model is to introduce opportunism to improve the spectrum utilization rate, which includes spectrum property right and dynamic spectrum allocation. Open * * * sharing mode, also known as spectrum sharing mode, opens spectrum to all users for * * * sharing, such as open * * * sharing mode of ISM frequency band. The core idea of hierarchical access model is to give oauth2.0 spectrum to unauthorized users, but to some extent, restrict the operation of unauthorized users so as not to interfere with authorized users. There are two kinds of spectrum underlay and spectrum filling. Spectrum allocation in cognitive radio is mainly based on two access strategies: ① orthogonal spectrum access. In orthogonal spectrum access, only one cognitive user is allowed to access each channel or carrier at a certain moment. After allocation, the communication channels between cognitive users are mutually orthogonal, that is, there is no interference between users (or interference can be ignored). ② * * * Enjoy spectrum access. In * * * spectrum access, cognitive users access multiple channels or carriers of authorized users at the same time, so users need to consider not only the interference tolerance of authorized users, but also the interference from other users. According to the interference tolerance constraints of authorized users, under the above two access strategies, it can be divided into the following two spectrum access methods: filled spectrum access and bottom spectrum access. For filled spectrum access, cognitive users wait for opportunity access? Spectrum hole? They only need to sell spectrum in time when authorized users appear, and there is no additional interference problem in sharing channels with authorized users. This method is easy to implement and does not need the existing communication equipment to provide interference tolerance parameters. In the underlay spectrum access mode, cognitive users and authorized users * * * enjoy spectrum, so it is necessary to consider the additional interference restrictions when * * * uses the channel.
Power control can reduce the power of the transmitted signal as much as possible without affecting the communication quality, thus improving the channel capacity and increasing the standby time of the user terminal. The design of power control algorithm in cognitive radio networks faces a multi-objective joint optimization problem. Because of the different requirements of different goals, there are many compromises. According to different application scenarios, the existing power control algorithms in cognitive radio networks can be divided into two categories: one is the power control strategy suitable for distributed scenarios, and the other is the power control strategy suitable for centralized scenarios. Most of the power control strategies in distributed scenarios are based on game theory, and some refer to the power control methods in traditional Adhoc networks, starting with centralized strategies, and then transforming centralized strategies into distributed strategies; However, the power control strategy in centralized scenario mostly takes advantage of the convenience of centralized information processing in base stations and adopts joint strategy, that is, combining power control with spectrum allocation or considering power control and access control together.
Adaptive transmission can be divided into service-based adaptive transmission and channel quality-based adaptive transmission. Service-based adaptive transmission is to meet the different QoS requirements of multi-service transmission, which is mainly realized in the upper layer, regardless of the actual transmission performance of the physical layer. At present, this adaptive transmission technology is considered in wired networks. Cognitive radio can optimize radio parameters and adjust related transmission strategies by using related technologies according to the perceived environmental parameters and channel estimation results. Optimization here means that the wireless communication system can meet the user's performance level while minimizing the resources it consumes, such as minimizing the occupied bandwidth and power consumption. Parameters that can be adjusted by physical layer and media control layer include center frequency, modulation mode, symbol rate, transmission power, channel coding method and access control method. Obviously, this is a nonlinear multi-parameter and multi-objective optimization process.
The existing layered protocol stack only considers the worst communication conditions when designing, which leads to the inability to effectively use limited spectrum resources and power resources. Cross-layer design coordinates the operation between layers by introducing and transmitting specific information in the existing layered protocol stack, so as to adapt to the complex and changeable wireless communication network environment and meet the different needs of users for various new business applications. The core of cross-layer design is to make each layer of layered protocol stack adaptively optimize the allocation of network resources according to the changes of network environment and user needs. In cognitive radio system, there are mainly the following cross-layer design technologies: in order to choose a suitable spectrum hole, the dynamic spectrum management strategy needs to consider the high-level QoS requirements, routing, planning and sensing information, and the interaction between communication protocols and the close combination of physical layers make the dynamic spectrum management scheme must be cross-layer. The spectrum shifting function needs to be combined with other spectrum management functions such as spectrum sensing, and the available frequency bands are determined by * * *. In order to estimate the impact of spectrum switching duration on network performance, it is necessary to know the information and perceptual delay of link layer. Network layer and application layer should also know this duration to reduce sudden performance degradation; In addition, routing information is also important for the route discovery process using spectrum switching. The performance of spectrum enjoyment directly depends on the spectrum sensing ability in cognitive radio networks, which is mainly the function of the physical layer. However, in the case of cooperative spectrum sensing, detection information needs to be exchanged between cognitive radio users, so cross-layer design between spectrum sensing and spectrum sharing is necessary. In cognitive radio system, because the available spectrum of each hop in multi-hop communication may be different, the topology configuration of the network needs to know the information of spectrum perception, and one of the main ideas of routing design of cognitive radio system is the combination of routing and spectrum decision.
Cognitive radio application scenario
Cognitive radio system can not only effectively use spectrum, but also has many potential capabilities, such as improving system flexibility, enhancing fault tolerance and improving energy efficiency. Based on the above advantages, cognitive radio has broad application prospects in both civil and military fields.
The improvement of spectrum efficiency can be achieved not only by improving the spectrum efficiency of a single wireless access device, but also by improving the storage performance of various wireless access technologies. This new spectrum utilization method is expected to improve the performance of the system and the economic value of the spectrum. Therefore, these * * * memory/* * enjoyment performance improvements of cognitive radio systems promote the development of new spectrum utilization modes, and make it possible to obtain new spectrum by * * * memory/* * enjoyment modes. The ability of cognitive radio system is also helpful to improve the flexibility of the system, including improving the flexibility of spectrum management, improving the flexibility of equipment operation in the life cycle and improving the robustness of the system. Fault tolerance is one of the main performance of communication system, and cognitive radio can effectively improve the fault tolerance of communication system. Usually, fault tolerance is mainly based on built-in testing, fault isolation and error correction measures. Another advantage of cognitive radio fault tolerance is that cognitive radio system has the ability to learn fault, response and error information. Cognitive radio system can adjust working parameters, such as bandwidth or signal processing algorithm, according to business requirements, so as to improve power efficiency.
What cognitive radio needs to solve is the utilization of resources, and its advantages in rural application can be summarized as follows. The use of radio spectrum in rural areas mainly occupies radio, television and mobile communication frequency bands. Its characteristics are that the occupation of radio frequency band is basically the same as that of cities, the utilization rate of TV frequency band is less than that of cities, and the occupation of mobile communication frequency band is less than that of cities. Therefore, considering from the frequency domain, the available frequency resources are richer than those in cities. The rural economy is generally less developed than that of cities, and the utilization rate of mobile communication is not as good as that of cities, except for the relatively fixed occupation of TV frequency bands. Therefore, the utilization rate of allocation frequency is relatively low. Because rural areas are vast and sparsely populated, mobile cells are limited by radiation radius, and there is no mobile communication frequency coverage in a large number of areas, especially in remote areas, and the available resources in frequency space are quite rich.
In a heterogeneous wireless environment, one or more operators operate multiple wireless access networks in different frequency bands allocated to them. Using cognitive radio technology, terminals are allowed to have the ability to select different operators and/or different wireless access networks, and some of them may also have the ability to support multiple synchronous connections on different wireless access networks. Because the terminal can use multiple wireless networks at the same time, the communication bandwidth of the application increases. As the terminal moves and/or the wireless environment changes, it can quickly switch to the appropriate wireless network to ensure stability.
In the field of military communication, the possible application scenarios of cognitive radio include the following three aspects. Cognitive anti-jamming communication. Because cognitive radio gives radio stations the ability to perceive the surrounding environment, they can extract the characteristics of interference signals, and then choose the appropriate anti-jamming communication strategy according to the electromagnetic environment perception information, the characteristics of interference signals and the requirements of communication services, which greatly improves the anti-jamming level of radio stations. Battlefield electromagnetic environment perception. One of the characteristics of cognitive radio is the integration of inductive environmental perception and communication. Because each radio station is both a communication radio station and an electromagnetic environment sensing radio station, it can be used to form an electromagnetic environment sensing network, which can effectively meet the requirements of all-weather, all-frequency and all-region electromagnetic environment sensing. Battlefield electromagnetic spectrum management. The electromagnetic spectrum of modern battlefield is no longer the traditional radio communication spectrum, and the static and centralized spectrum management strategy can no longer meet the flexible needs of modern warfare. Battlefield electromagnetic spectrum management based on cognitive radio technology endows various operational elements with spectrum sensing ability, which enables spectrum monitoring and spectrum management to be carried out at the same time, greatly improving the coverage of spectrum monitoring network and broadening the coverage of spectrum management.
Concluding remarks
How to improve the spectrum utilization rate to meet the bandwidth demand of users; How to make the radio intelligent, so that we can independently discover when, where and how to use wireless resources to obtain information services; How to effectively obtain information from the environment, learn, make effective decisions and make adjustments are all problems to be solved by cognitive radio technology. The introduction of cognitive radio technology provides strong support for realizing wireless environment awareness, dynamic resource management, improving spectrum utilization and realizing reliable communication. Cognitive radio has broad application prospects and is another milestone in the development of radio technology.
Computer Paper Model 2: Design and Research of Remote Wireless Management and Control System
1 Introduction
With the development of China's space industry, the task undertaken by survey ships is high density and intensity, which leads to more and more arduous task preparation during the docking period, facing the reality of many assessment items, short assessment time and multi-ship coordination. How to improve the efficiency of benchmarking and ensure the safety and reliability of benchmarking has become an urgent problem to be solved. Due to the confidentiality requirements, the original remote calibration control system can not access the existing network, and the cost of laying a private network is high and the cost performance is low, so it is not the first choice. In recent years, wireless communication has become the fastest developing and most widely used technology in the field of information communication, widely used in the fields of family, agriculture, industry, aerospace and so on, and has become an indispensable part of social life in the information age [1]. This technology also provides support for solving the remote control problem of the calibration equipment of the survey ship. In this paper, by comparing the commonly used medium and long distance wireless communication modes, wireless bridges are selected and the networking mode of bridging relay is adopted. By developing the network control module and corresponding control software of the remote equipment, the effective safety control of the remote equipment by the survey ship is realized.
2 Comparison of wireless communication modes
Wireless communication technology is a communication mode that uses electromagnetic wave signals to spread information in free space. According to technical forms, it can be divided into two types: one is cellular access technology, such as cellular digital packet data, general packet radio transmission technology, EDGE and so on. Second, LAN-based technologies, such as WLAN, Bluetooth, IrDA, Home-RF, micro-power short-distance wireless communication technology, etc. Communication technologies in ISM band (such as ZigBee and data transmission modules in other frequency bands) and wireless network technologies (such as GSM, GPRS and wireless bridges) are commonly used in long-distance wireless communication. The communication frequency of digital transmission module based on ISM frequency band is public frequency band, and there is no restriction on product development, so it develops very rapidly and is widely used. Especially in recent years, the emerging ZigBee technology, because of its low power consumption, low complexity and low cost, especially self-organizing networking, can flexibly complete network links without limiting the number of devices in the network segment, and has been applied in the development of network systems such as smart home and wireless meter reading [2]. However, for the development of the system, it is necessary to develop the hardware modules of the control point and the controlled point separately, and configure the network environment through software, which is not the best scheme for the development of the system.
GSM and GPRS, two wireless mobile communication technologies, have become an indispensable part of people's daily life and work, and are also widely used in wireless positioning, remote control and other fields [3]. However, due to confidentiality, communication costs, development costs and other factors, it can not be applied to the development of this system. Wireless bridge provides favorable support for the research and development of the system with low cost and high efficiency, and is the first choice for the development of the system. Wireless bridge is a bridge of wireless network, which can bridge the communication between two or more networks, and it is also a branch of wireless access point. The wireless bridge works in 2 minutes? 4GHz or 5? 8GHz band, no need to apply for a wireless license, so it is more convenient to deploy than other wired network equipment, especially suitable for short-distance and long-distance communication in cities.
3 system design
The remote control system aims to ensure the effective control of the remote calibration equipment by the measuring ship, including the switch of the calibration equipment and the collection of state parameters. It is mainly composed of the survey ship control microcomputer, calibration equipment, network control module, main control microcomputer and wireless bridge. The workflow is as follows: the control microcomputer or main control microcomputer of the survey ship sends out control instructions, and the information is spread through the wireless bridge; The network control module receives and analyzes the instruction, and sends it to the calibration device through the serial port according to the data format specified by Modbus protocol, and the calibration device responds to the control instruction and executes it; The network control module sends query instructions regularly, and the collected state data is packaged and wirelessly sent to the remote control microcomputer, which is convenient for operators to monitor. The network communication protocol adopts UDP mode, and the control microcomputer and main control microcomputer of the survey ship only need to send or receive UDP packets according to a certain data format. Network control module is the core component of the system, and it is the focus of this paper's research and design. At present, the commonly used network chips mainly include ENC28J60 and CP2200. In this paper, C28J60 is selected, and the hardware circuit based on STC89C52RC single chip computer is designed and processed. Through the development of network information processing software module, the functional requirements of network information interaction are met; By developing Modbus serial port protocol software module, the monitoring function of calibration equipment is satisfied and the system design goal is realized.
3. 1 networking mode
Wireless bridge has three working modes, namely point-to-point, point-to-multipoint and trunk connection. According to the control requirements of the system and environmental factors, the system adopts relay connection mode, and its network topology is shown in figure 1. It can be clearly seen from the figure that two wireless bridges are arranged at the remote control end of this relay connection mode, which communicate with the main control point and the client respectively, and complete data interaction through the network control module, thus completing networking.
3.2 Safety precautions
Because it is an open design, wireless network security is a problem that must be considered. The characteristics of the system are irregular or all-weather startup, confidential data only have frequency parameters, and the controlled equipment itself has protection measures (protocol protection). Therefore, the design of the system focuses on preventing access points and attacks, and the measures taken include login password facilities, network key setting, fixed IP, and dynamic encryption of confidential data in data structure. , thus preventing? Hacked? . At the same time, network lightning protection device is adopted to prevent lightning damage.
3.3 Design of Network Control Module
3.3. 1 Hardware design
The function of network control module is to receive command information and send status information, and realize information interaction with calibration equipment through serial port. Its hardware circuit is mainly composed of MCU (microcontroller), ENC28J60 (network chip), Max232 (serial chip) and peripheral circuits, and its electrical schematic diagram is shown in Figure 2. The core of hardware design is the choice of MCU and network chip. The STC89C52RC microcontroller selected by the MCU of this system is a CMOS8-bit microcontroller with low power consumption and high performance, which can be downloaded directly through the serial port, providing a highly flexible and super effective solution for many embedded control application systems. Tapestry C28J60 is a highly integrated Ethernet control chip produced by M-microchip company. Its interface conforms to IEEE802.3 protocol, and only 28 pins can provide corresponding functions, which greatly simplifies the related design. Although C28J60 provides SPI interface, communication with MCU is realized through two interrupt pins and SPI. The data transmission rate is 10 mbit/s, ENC28J60 conforms to all specifications of IEEE802.3, adopts a series of packet filtering mechanisms to limit incoming packets, and provides internal DMA module to realize fast data throughput and IP checksum calculation supported by hardware [4]. Wang C28J60 uses HR9 1 1 102A as its external network interface. Built-in network transformer, resistance network and status display lamp have the characteristics of signal isolation, impedance matching and interference suppression, which can improve anti-interference ability and transceiver stability.
Software design.
The software design of network control module mainly includes two parts. The first is the driver programming of ENC28J60 based on SPI bus, including the definition and initialization of Ethernet data frame structure and data transceiver. The second is Modbus protocol, and its software flow is shown in Figure 3.
Driver programming
(1) Ethernet data frame structure The length of an Ethernet frame conforming to IEEE802.3 standard is between 64 ~ 15 16 bytes, which is mainly composed of target MAC address, source MAC address, type/length field, data payload, optional padding field and cyclic redundancy check. In addition, when a data packet is sent through an Ethernet medium, a 7-byte preamble field and a 1 byte frame start delimiter are appended to the beginning of the Ethernet data packet. The structure of Ethernet packet is shown in Figure 4. (2) driver programming1) register reading and writing rules of ENC28J60 Because enc28j60 chip adopts SPI serial interface mode, the rule of reading and writing internal registers is the first operation code+register address.
ModBus protocol flow
The data communication of ModBus protocol in this system adopts RTU mode [5]. As the master node, the network control module is connected with the slave node (calibration equipment) through the serial port. The master node sends the inquiry command to the slave node periodically, and sends the equipment status information to the master node according to the response command of the slave node. When the network data is detected, the command is parsed from the data packet received by ENC28J60, and the corresponding function code and data framing are sent to the slave node according to the Modbus data frame structure; The corresponding slave node responds to the control command to set the device parameters.
4 system debugging and verification
The test and debugging environment is arranged according to the figure 1, which mainly includes five wireless bridges, 1 main control point, two clients, 1 network control module board and calibration equipment. The main tests include network communication effect, network control ability and simple safety protection test. Test conclusion: The network connection is reliable, each control point can safely control the remote equipment, and has certain safety protection ability, which fully meets the control requirements of the remote equipment.
5 concluding remarks
Based on the actual demand, this paper compares the current popular wireless communication technologies, and chooses wireless bridge to realize the networking of remote control system. By developing network control module and corresponding control software, a set of remote control equipment system for measuring ship is developed. The application of several survey ships shows that the wireless bridge networking completely meets the system design requirements, and has the advantages of high security, high reliability and high expansibility, which plays an important role in the increasingly heavy support task. The wireless networking mode and hardware circuit design scheme adopted by the system have certain reference value for other related control fields.