Custom Piezoelectric Components The piezoelectric ceramic sound-generating element, especially a lead-free piezoelectric ceramic sound-generating element, is mainly composed of metal flakes and piezoelectric ceramic flakes. The sound pressure generated by this new structure piezoelectric sounder is proportional to the number of piezoelectric ceramic sheets. By increasing the number of piezoelectric ceramic sheets, the required large sound pressure is easily achieved. Custom Piezoelectric Components,PZT Elements Soldered Wires,Element of Piezoelectric,Piezoelectric Elements Crystal Zibo Yuhai Electronic Ceramic Co., Ltd. , https://www.yhpiezo.com
1 GPRS application analysis in public security police work
GPRS is the abbreviation of General Packet Radio Service and is a new bearer service developed on the existing GSM system. Mainly add some nodes in the existing GSM network, the gateway GPSRS supports the node GGSN, and serves the GPRS support node SGSN. The GPRS network implements various functions that are beneficial to high-speed data transmission such as multi-slot bundling and data compression. Its main network unit functions are divided into the following parts:
(1) Packet control unit (PCU): mainly used to complete the conversion of wireless data blocks, send packet services to SGSN, and voice services to MSC (mobile switching center);
(2) SGSN: performs functions such as mobility management, security functions, access control, and routing;
(3) GGSN: responsible for providing the interface between GPRS PLMN (public land mobile communication network) and external packet data network, and providing the necessary inter-network security mechanism (such as firewall);
(4) Border gateway (BG): The border gateway is used for the interconnection of GPRS backbone networks between PLMNs, and it should have basic security functions;
(5) Billing gateway (CG): communicates with billing entities in the GPRS network to collect billing data records sent by each GSN (GPRS service support node);
(6) Domain name server (DNS): responsible for providing the domain name resolution of SGSN, GGSN and other network nodes within the GPRS network and the resolution of APN (access point).
Its application characteristics in police work are mainly reflected in the following aspects:
(1) Wide network coverage: GPRS supports the most widely used IP protocol and X.25 protocol on the Internet. It can provide global seamless access to the Internet and other networks anytime, anywhere, and truly realize the mobile office of public security personnel.
(2) High resource utilization rate: In the network selection of the mobile police system, if a dedicated network channel is established separately through the public security system, the cost is too high. GPRS is developed on the basis of the original GSM network and introduces a packet-switched transmission method. Users only occupy resources during the period of sending or receiving data. According to the actual communication data flow as a charging standard, resource utilization is improved.
(3) Data bandwidth: The internal wireless intercom network can not meet the bandwidth requirements of the network. The data transmission speed of GPRS can reach 57.6 Kb / s, and the highest can reach 171 Kb / s, which can well meet the real-time and sudden work of public security. Hair requirements.
(4) Safe and reliable transmission: In the process of data transmission, IP data packets are divided into several fragments by packet switching technology, and are transmitted to the destination end through different routes in a store-and-forward manner to form complete data. Data packets can be sent continuously, thus ensuring the reliability of real-time transmission of public security work.
2 System design
The functions of the public security traffic police mobile system are mainly divided into the following parts:
Violation Penalty System Registers driver violation information and punishment information, mainly including fines, scoring, suspension, detention, revocation, and compulsory measures, and is fully adapted to violations on the spot punishment procedures and general punishment procedures and procedures for handling mandatory measures.
Mobile phone photo violation According to the violation information, the vehicle and the individual are photographed and stored, the violation information is recorded, the corresponding violation owner is notified, and the corresponding vehicle driver is given a corresponding penalty. The penalty data is entered into the violation penalty system, and the penalty ticket is printed in real time.
The reconciliation system automatically compares the payment at the collection point with the penalty stub penalty. The violation payment has been accurately and quickly counted; the payment point statistics, the actual payment statistics and the difference between the two are used to facilitate the payment point Supervision.
2.1 System network topology design and implementation
The public security traffic police mobile police communication system is based on a cross-wireless mobile platform, adopting an internal and external network separation architecture, and a multi-channel internal and external network isolation technology to ensure the security of public security private network data while transmitting data at high speed. The system consists of mobile terminal, mobile communication network, wireless system isolation local area network, public security intranet 4 parts:
Mobile terminals Mobile phones, PDAs and mobile devices with certain calculation, storage, and transmission functions. The public security traffic police collect, query, and compare information through the software system installed on the mobile terminal.
The mobile communication network is responsible for the communication between the mobile terminal and the wireless system isolated LAN. The mobile terminal initiates a wireless request, and the data from the mobile terminal is shunted through the base station, and the data transmission and reception between the mobile station and the GPRS backbone network are completed through the SGSN. GGSN acts as a gateway between the GPRS network and the public data network, and connects to the Internet network through it. Then filter through the firewall to enter the public security extranet.
The wireless system isolation local area network consists of an external network server that stores an external network database, an authentication server, an isolation / request forwarder, and a physical security gatekeeper. The data request sent by the mobile terminal is connected to the external network server through the existing GPRS network and the repeater, and the result of the data request is returned to the mobile terminal in real time through the XML data format. The physical isolation gatekeeper connects the public security intranet server and the external network server between the two systems. There is no physical connection for communication, logical connection, and information transmission protocol. The data packets of the external network server are decomposed and reorganized into static data. The static data is reviewed for security, and the data confirmed to be safe enters the public security intranet server.
The public security intranet is composed of the core database inside the public security (vehicle information management database, stolen vehicle information database, three escape / high-risk personnel information database, mobile personnel information database, resident information database), intranet server, isolation / request forwarder And data interface module. Through the secure isolation gatekeeper, the database of the public security internal network and the database of the external network server are synchronized in real time in one direction, and the core database information is transmitted to the external network server to prevent the possibility of external attacks on the public security internal network. The GPRS network topology is shown in Figure 1. 
2.2 System software structure design and implementation
The mobile wireless traffic police system software is composed of client software design, server software design, module management system and background database.
The client software is designed using J2ME. J2ME takes full advantage of the platform independence of the Java language to run across platforms, supports network protocols such as HTTP and TCP, and can directly access the Internet. Supporting highly efficient distributed computing is conducive to making full use of resources on mobile devices. J2ME provides the MIDP 2.0 specification, which requires all MIDP devices to implement the HttpConnecTIon interface, so that all devices that comply with the MIDP specification can communicate with each other under the HTTP protocol. Through this interface, the client program communicates with the server in real time. In order to reduce the interaction with the server, the data dictionary information is stored on the client, which improves the performance of the system.
The software of the client is complicated and has many interfaces, so the reusability of the software needs to be considered, and the current system is only the traffic police version, which will be expanded to the fire alarm version and the civilian police version in the future. low efficiency. Therefore, the design pattern of the system adopts the MVC (model view controller) pattern, which divides the application of the system into three layers: the model layer, the view layer, the control layer, and the model layer. The model layer encapsulates the core data of the system and the functions of the system. The view layer explains the model layer and displays data and system functions through the interface. The control layer defines application behavior and coordinates the model and views. Separating these three layers is conducive to the division of labor of different modules and improves the scalability and robustness of the program.
For server-side program development, choose Servlet and JavaBean. Servlet establishes a dynamic mode based on main request and response with the client through HTTP. The client sends an HTTP request to the server through the GPRS wireless communication network, the server receives the request response and calls the corresponding JavaBean business logic module, accesses the mobile traffic police background database through JDBC, and returns the query processing result to the client through the Servlet for display.
The mobile traffic police system client frequently requests a database connection, which not only consumes system resources, but also may cause the system to crash. Therefore, the server side has established a database connection pool, put a certain number of connections in advance, and take it from the connection pool when needed. Realize multiple requests to share resources and improve database access efficiency.
The collection and comparison of person photos and vehicle photos is an important part of public security work. The pictures sent by the server to the client are stored in the corresponding fields of the database in the form of large objects (Blob), and the images are correspondingly processed on the server. With enhanced processing, the public security police can print the owner's certificate, ticket information, and inquire and compare the photos of the characters and vehicles through the Bluetooth printer on the spot according to the needs, to meet the real-time and mobility requirements of the public security traffic police.
2.3 Module management system and background database
The module management system includes a police officer authority management system and a system update module. The police officer authority management grants different police officers different access rights to the system. The system update module means that when a module function of the system changes or a new function is added, different police officers can download different updated versions in real time through this module. The back-end database uses Oracle 9i database. Oracle 9i is an object-oriented database system that uses an object / relational model to not only process traditional table structure information, but also support other multimedia data types, such as text, video, and graphics. Using advanced network technology and distributed structure, data and applications can reside on multiple computers, while ensuring that the communication between computers is transparent. Provides automatic backup and recovery functions, improving good security.
2.4 System implementation
The system was tested on-site at Nokia N72 through China Mobile's GPRS network and compared with the cable simulator. The results are shown in Table 1. 
It can be seen from the actual measurement results that the operating speed of the system is within the acceptable range, which can meet the functional requirements of the public security business. Compared with the original manual method, it saves time and effort. The user-friendly interface is convenient for users to use and maintain and upgrade the later system, which improves the efficiency of data exchange between the public security traffic police and the center
3 Conclusion
The mobile police system described in this article passed the test on Nokia N72. The system comprehensively utilizes wireless mobile storage technology, embedded database technology, network security technology, etc. The system has real-time query vehicle information, stolen vehicle query, vehicle owner information collection and query, real-time printing of vehicle owner information and fines, traffic police management and other functions, the system improves the efficiency of public security traffic police. With the comprehensive promotion of the third generation mobile communication (3G), the network transmission rate will be greatly improved, and the application prospect of the system will be very broad.
Based on the GPRS wireless transmission network, this article designed and developed a set of public security traffic police mobile police system that exchanges data with the public security system data center in real time with the help of J2ME technology and Oracle 9i database, and finally tested it through a mobile phone terminal. The use of the system Will greatly improve the efficiency of front-line traffic police management and case handling.