1. Introduction With social development and advancements in communication technology, the demands for mobile target monitoring are increasing. It's not enough to simply know the location of a moving target; real-time monitoring and processing of video images, alarm information, and operational status are also required. For example, mobile monitoring and positioning systems can assist in the management of long-distance buses. The command center can determine the bus's location by analyzing the GPS data sent by the bus, judging whether it is speeding. If the bus malfunctions, encounters an accident, or is hijacked, it can promptly notify the command center, which in turn notifies transportation, public security, and hospital departments for emergency response. Installing cameras on buses can also effectively prevent crimes during travel. On the other hand, drivers can use the command center to understand the geographical information, weather conditions, and traffic conditions ahead. Furthermore, mobile monitoring and positioning systems have broad application prospects in areas such as fishing vessel operations, urban taxi dispatching, public security patrols, and bank armored vehicle monitoring. Mobile surveillance and positioning systems have developed alongside the maturation of GPS and wireless communication network technologies. In the early 1990s, when GPS technology was just entering practical application, GPS-based mobile tracking and monitoring systems began to appear on the market. However, due to limitations in wireless communication network technology, system deployment was small-scale and costs were high, hindering widespread adoption. In recent years, various dedicated wireless communication networks, trunked radio networks, satellite data communication networks, and digital cellular mobile communication networks have developed rapidly, significantly enhancing their data carrying capacity. Furthermore, GPS technology has become more mature. Currently, 12-channel GPS receivers are relatively inexpensive. On May 1, 2000, the US government announced the cancellation of GPS SA (Standalone) policy, allowing GPS receivers to achieve a positioning accuracy of approximately 25 meters. For these reasons, mobile surveillance and positioning systems based on GPS and wireless communication networks have experienced rapid development worldwide, demonstrating strong growth momentum and enormous market potential. GPS technology and wireless communication network technology are two key elements of mobile monitoring and positioning systems. GPS receivers or OEM cards are now commercially available, with very small sizes and convenient data interfaces, providing standard serial port data output. Wireless communication networks, however, are diverse, with varying construction costs and system capacities. Available communication networks include trunked radio networks, satellite data communication networks, and mobile communication networks. 2. Selection of Communication Networks for Mobile Monitoring and Positioning Systems Wireless communication networks are an important component of mobile monitoring and positioning systems, and can be divided into two main categories: private wireless networks and public wireless communication networks. Private wireless networks, satellite communication networks, and mobile communication networks are some of the more common forms. 2.1 Private Wireless Networks Private wireless networks are wireless communication networks specifically built for mobile monitoring and positioning systems. They have their own switching centers, base stations, and monitoring platforms. The disadvantages are higher network construction costs and limited coverage area. However, private wireless network systems are flexible to modify, have strong resilience, and are mobile, making them suitable for specialized fields such as flood control and disaster relief command systems and military combat command systems. 2.2 Satellite Communication Networks Satellite communication includes three types: geostationary orbit satellite communication, medium Earth orbit satellite communication, and low Earth orbit satellite communication. Satellites act as relays, while earth stations serve as base stations or connect to users. The advantages of satellite communication are its large coverage area, enabling global connectivity, and its insensitivity to weather and transmission distance. It is particularly suitable for areas where general wireless networks cannot reach, such as deserts and forests. Furthermore, in the maritime field, satellite communication network-based monitoring and positioning systems can be used for navigation and real-time monitoring of ships, allowing for timely response to pirate attacks and maritime disasters. In the aviation field, monitoring and positioning systems in civil aircraft operations can prevent mid-air collisions; in the event of a hijacking, onboard cameras can provide real-time information on the situation on board; and in military operations, this system can be used to form an airborne command platform. The disadvantages are the complexity and high cost of the system's terminal equipment, hindering its widespread adoption. 2.3 Mobile Communication Networks In recent years, mobile communication has developed rapidly, from analog AMPS networks to digital cellular GSM networks, to CDMA mobile communication networks. Now, some countries, including Japan, have proposed the concept of fourth-generation mobile communication networks (4G) and have begun development and research. Compared to private wireless networks or satellite communication networks, mobile communication networks are more widespread. Building monitoring and positioning systems based on mobile communication networks has advantages such as large coverage area and low network construction costs. Utilizing the data access function of mobile communication networks to carry out value-added services can also improve network resource utilization. However, the data transmission rate of mobile communication networks is generally low. To increase the data transmission rate, the existing network needs to be upgraded. For example, using CDPD (Packet Data Switching) technology, packet data services can be provided on analog cellular AMPS networks with a channel rate of 19.2 kb/s. In digital cellular communication networks, the data rate of GSM networks is only 9.6 kb/s. When GSM networks are improved using GPRS (General Packet Radio Service) technology or EDGE (Enhanced Data Rate) technology, they will provide data rates of 115.2 kb/s and 384 kb/s respectively. Furthermore, both IS-95B and CDMAOne have enhanced mobile data service capabilities, while CDMA2000 can provide data rates up to 2 Mb/s. Utilizing mobile communication networks to build mobile monitoring and positioning systems is convenient to deploy and maintain, covering all areas reachable by mobile phone signals, making it ideal for applications such as vehicle and ship dispatching, 110 emergency call command, and railway train wireless dispatching. Besides the communication networks mentioned above, there are also digital trunking communication networks and cordless telephone communication networks (including DECT systems, PHS systems, etc.), all of which can be used to transmit monitoring and positioning data. 3. Design of a Mobile Monitoring and Positioning System Based on GSM Through the comparison of the above communication networks, mobile communication networks are the most economical and easily deployed method. While the third-generation mobile communication network CDMA has high data transmission capabilities, it is currently still in the experimental stage. In contrast, GSM digital cellular mobile communication networks are already very widespread domestically and internationally, with the widest market application, the largest coverage area, and the most mature technology. Therefore, utilizing GSM mobile communication networks to build mobile monitoring and positioning systems is currently a more reasonable choice. There are three methods for transmitting monitoring and positioning data through the GSM mobile communication network: transmission via voice channel, transmission via SMS (Short Message Service), and transmission via the improved high-speed data channel of GSM. 3.1 Design Method for Transmitting Data via GSM Voice Channel Transmitting data via the GSM voice channel is similar to transmitting data over a regular telephone line. Data communication is achieved through modem modulation and demodulation at both ends. This method is technically mature, widely applicable, and can be used within the coverage area of ​​the GSM network. The disadvantages are that dialing is required before data transmission, resulting in a relatively long call setup time, typically around 10 seconds, and the communication cost is the same as mobile phone charges, making it expensive. A mobile monitoring and positioning system established using this method is shown in Figure 1. The equipment composition of the mobile terminal is shown in Figure 2. In Figure 2, the GPS receiver of the mobile terminal acquires location and speed information, the camera captures image information, the microphone transmits voice, and the alarm device provides alarm information. These are sent to the data interface device for format conversion, modulated by the modem, and then transmitted to the GSM mobile network via the GSM mobile phone. The system monitoring center is connected to the GSM network switching center via trunk lines. These trunk lines provide voice channels via telephone lines, fiber optics, or microwave. Data from mobile terminals is demodulated and processed by the monitoring center's modem before being sent to the corresponding subsystems. For example, GPS information is sent to the GIS (Geographic Information System) subsystem, images and voice are sent to the multimedia display subsystem, and alarm information is sent to the alarm processing subsystem. The monitoring center can control each mobile terminal through the dispatch and command subsystem, while the network management subsystem is responsible for the operation and management of the entire network. When designing a mobile monitoring and positioning system using GSM voice channels, the number of channels and service functions can be added or deleted arbitrarily according to the number of mobile terminals and actual needs. Simple point-to-point mobile monitoring systems can also be formed, such as for home monitoring. 3.2 Design Method Using GSM SMS Communication SMS (Short Message Service) is a value-added service of the GSM network. It transmits data through control channels and supports various methods such as point-to-point messaging and message broadcasting. A mobile monitoring and positioning system that transmits data via SMS is shown in Figure 3. Unlike Figure 1, the mobile terminal's data is sent entirely to the Short Message Service Center via SMS, and the system monitoring center obtains the data from the Short Message Service Center through a relay line (such as DDN). Transmitting data via SMS has the following advantages: (1) Short channel setup time and fast data transmission rate; (2) Does not occupy the voice channel, and does not affect data transmission during calls; (3) Low communication costs due to not occupying the voice channel; (4) Point-to-multipoint data transmission can be provided through the Short Message Broadcast service; (5) Convenient system expansion. On the other hand, since the control channel's transmission rate is 781 kb/s, the data transmission rate cannot be very fast. SMS is also limited by message length; the length of a point-to-point message is 140 bytes, and the length of a message broadcast service is 82 bytes. This determines that the transmitted data cannot be too long, making it suitable for systems with small amounts of information but frequent communication. Furthermore, as system capacity increases, SMS will also increase the burden on the GSM network control channel. 3.3 Design Method for High-Speed ​​Data Channel Communication using GSM Among the two data transmission methods mentioned above, the data rate is relatively slow, only suitable for transmitting short data such as GPS data, alarm information, and control information. Transmitting surveillance images or downloading geographic information to mobile terminals is difficult. Therefore, it is necessary to further improve the data transmission rate of the GSM communication network. GRPS (General Packet Radio Service) is a recently emerging technology. By adding protocol gateways and modifying a few devices on the existing GSM network, it can provide data transmission rates up to 115.2 kb/s. GRPS supports protocols such as X.25 and TCP/IP. Many large companies worldwide are currently developing GRPS functionality. In China, Eastern Communications and Motorola are collaborating on the development of GRPS mobile phones and related equipment. Another technology to improve GSM data transmission rates is called EDGE (Enhanced Data Rate), which can support data rates of 384 kb/s. Among the above three design methods, using the high-speed data channel provided by GSM's GPRS or EDGE is a more ideal method. It is currently under research and development. GSM's voice channel is the most widely used, but the communication cost is high. Using SMS service to transmit data is the most economical and reasonable method, and SMS service is gradually becoming more widespread. 4 Business functions of mobile monitoring and positioning system The mobile monitoring and positioning system designed based on GSM communication network can provide the following functions: (1) Positioning function Through the GPS information sent by the mobile terminal, the monitoring center can track and locate the mobile target in real time, monitor the speed and running status of the mobile target, and display the movement trajectory on the map in real time through the GIS system; conversely, the monitoring center can query relevant information of vehicles in the area through the map, such as vehicle license plate, unit name, driver name, speed, etc. (2) Dispatch and command function Because the monitoring center has the geographical location and running status of each mobile target, it can dispatch and command as needed. For example, in taxi operation, if this system is used, the monitoring center can notify nearby vehicles to provide service according to the customer's call. (3) Alarm Function The alarm information sent by the mobile terminal is divided into two types: self-fault alarm information and emergency alarm information. Taking long-distance passenger bus as an example, self-fault alarm includes vehicle oil leakage, abnormal engine status, etc.; emergency alarm information includes road and bridge collapse, traffic accident, robbery, etc. when encountering an alarm. When an alarm occurs, the monitoring center can classify and process the alarm information of the bus and notify the traffic and public security departments in a timely manner by connecting with 110 and 120. (4) Video Monitoring Function By installing a camera, the monitoring center can view the video image of the moving target at any time and record it. For example, it can monitor whether the long-distance passenger bus driver has illegally solicited passengers or refused to carry passengers on the way. If a robbery, theft or other criminal event occurs in the vehicle, the video playback can be used to assist in solving the case, etc. (5) Call Function When using SMS or high-speed data channel to transmit 64 data, the mobile terminal also has normal GSM digital telephone function during data transmission. (6) Guidance Function Installing a GIS system in the mobile vehicle can realize the vehicle self-guidance function and roaming nationwide. (7) Historical data query function: Users can query the historical information of mobile terminals through the records of the monitoring center, such as querying the location, speed, status and other data of vehicles at a certain time in the past, and can play back the running trajectory. In actual system design, the system can be simple or complex for different purposes, from point-to-point monitoring to monitoring and positioning systems with hundreds of mobile terminals. Business functions such as GPS positioning and video image monitoring can also be added or deleted as needed. 5 Conclusion: Mobile monitoring and positioning systems have great market potential in China. In recent years, different forms of mobile monitoring and positioning systems have been built throughout the country, such as GPS vehicle tracking systems, mobile command and dispatch systems, and vehicle navigation systems. In May 2000, Shanghai built a public mobile GPS system, which uses GSM as the communication platform to provide GPS positioning and monitoring information services to users in Shanghai and East China. Users only need to purchase GPS vehicle equipment to join the network. Beijing has also built a GSM/GPS satellite positioning service system, which is based on satellite communication and can provide high-precision three-dimensional positioning information. It will open static vehicle anti-theft and dynamic vehicle tracking services to the public. In addition, many domestic communication network companies can provide GPS receivers, GSM/GPS integrated machines, GIS systems, system monitoring software platforms and complete system solutions. However, due to their early stage, there are still many problems in system design, such as: the monitoring software functions are relatively backward and the dynamic data processing capability is poor; the data communication format is not unified and products from different manufacturers are incompatible; since the monitoring data is transmitted wirelessly, most systems do not take encryption measures, and the monitoring and positioning information can be easily intercepted. [b]References[/b] ［1］ Zhao Rongli. Digital Cellular Mobile Communication System［M］. Beijing: Electronic Industry Press, 1997. ［2］ Ding Jin, Wu Wenhao, et al. Digital Wireless Local Loop System［M］. Beijing: Electronic Industry Press, 1997. ［3］ Guo Feng, et al. Wireless Local Area Network［M］. Beijing: Electronic Industry Press, 1997. ［4］ Fan Changxin, et al. Communication Principles［M］. Beijing: National Defense Industry Press, 1981. ［5］ Jia Yutao, et al. Practical Mobile Radio Communication [M]. Beijing: National Defense Industry Press, 1995. Editor: He Shiping