GPS-based vehicle navigation and GPRS network monitoring

Introduction
In recent years, the demand for effective monitoring, emergency rescue and provision of various information services for highly mobile and numerous moving targets has been particularly prominent in industries such as passenger transportation, public security, banking, and logistics. The emergence of General Packet Radio Service (GPRS) enables people to conduct nationwide, real-time, and all-weather monitoring and dispatching of moving targets. Combining GPS positioning technology with GPRS has broad application prospects.

System Structure
The entire positioning, navigation and monitoring system is mainly composed of two parts: the vehicle-mounted terminal (including a micro industrial computer, touch screen, GPS receiving module, GPRS communication module and power supply, etc.) and the monitoring data center DSC (TCP/IP network server).
The GPS module of the vehicle terminal receives the position, time and other data of the global positioning satellite in real time. On the one hand, it is sent to the micro single-board computer in the vehicle to obtain the current location of the vehicle and display it on the electronic map; on the other hand, the data will be sent through the GPRS terminal The module is sent to the remote monitoring center server, so that the monitoring center can obtain the location information of all vehicles in real time, providing a basis for vehicle safety monitoring and remote dispatching.

Vehicle-mounted terminal
The hardware composition of the vehicle-mounted terminal is shown in Figure 1.

Figure 1 Principle diagram of vehicle terminal hardware composition

GPS receiving module
GPS consists of three parts, the space constellation part, the ground monitoring part and the user receiver part. The space constellation consists of 24 navigation satellites, which is equivalent to providing 24 known space points. The ground monitoring part is used to monitor the status of satellites and correct satellite orbit information. The user receiver is used to receive satellite signals and complete signal analysis and calculation to obtain necessary navigation and positioning information.
This article uses Trimble's Lassen SQ/IQ series GPS receiver module. The data formats supported by this module include TSIP and NEMA0183. In current software systems, NEMA0183 format data is usually used. The NEMA 0183 protocol allows a signal source to send data serially over a twisted pair to one or more receivers.

The data from the GPS module of the micro industrial computer
is directly sent to the micro industrial computer through the RS-232 serial port. Through the electronic map software running on the industrial computer, the current location of the vehicle and each major geographical location can be displayed. Micro industrial computers not only have all the functions of ordinary computers, but also have a high degree of integration, are small in size, light in weight, and easy to install.

GPRS communication module
The vehicle terminal is embedded with the GPRS communication module, which sends the location information of the GPS receiving module to the remote database monitoring center in real time, realizing the monitoring and dispatching of all vehicles.
As a monitoring and dispatching system, we must first consider requirements such as monitoring coverage, real-time performance, dispatching business, vehicle capacity, refresh rate, etc., select appropriate wireless data links and electronic maps, and develop corresponding business software. The GPRS/IP/TCP/UDP protocol stack can realize real-time exchange of data and has the largest bandwidth among existing public wireless communication systems. Compared with the currently popular short message transmission method, it can achieve the same data length and the same time interval. Under this method, the communication cost is 1/6 of the short message method, or even less. This article uses the GPRS DTU H7000 series wireless communication module of Shenzhen Hongdian Company to realize GPRS network connection and data transmission. When the wireless communication module logs into the GPRS network, the location information of the GPS receiving module will be sent to the remote monitoring center in real time for monitoring and dispatching.

Monitoring center software design
The monitoring center is a network server with a public IP address. By writing the monitoring system software of the data center (mainly composed of communication modules, electronic map databases, vehicle information databases, etc.), the monitoring center will receive vehicle-mounted terminals in real time. The data sent through the wireless communication module is analyzed and stored, and the location and movement status of all vehicles are displayed on the electronic map. And provide prompts and alarms for different situations.
The monitoring center can also use WebGIS technology and use C/S or B/S architecture. The monitoring center and data server can be in different physical locations. Since data servers have high requirements for equipment reliability and corresponding operation and maintenance, from an economic perspective, building a self-built data server has high requirements for both hardware and software. You can use the current network services of .NET technology to access the data server through the local monitoring center to obtain data information, send commands, etc.
This article uses Microsoft Visual C#.NET as the development platform and the dynamic development library of Shenzhen Hongdian GPRS module. The dynamic development library provides some operating functions used in the GPRS wireless communication process. The important structures in the development package are as follows:
1. Terminal module registration information interface structure
typedef struct GPRS_USER_INFO
{
char m_userid[12]; //Terminal module number
uint32 m_sin_addr; //The proxy host IP address of the terminal module entering the Internet
uint16 m_sin_port; // The terminal module enters the Internet's proxy host IP port
uint32 m_local_addr;//The terminal module's IP address in the mobile network
uint16 m_local_port;//The terminal module's IP port in the mobile network
char m_logon_date[20]; //Terminal module login time
char m_update_date[ 20]; //Terminal module update time
uint8 m_status; //Terminal module status
}user_info;
2. Data packet interface structure
typedef struct GPRS_DATA_ RECORD
{
char m_userid[12]; //Terminal module number
char m_recv_date[20]; // The time when the data packet was received
char m_data_buf[1024]; //Storage of the received data
uint16 m_data_len; //The length of the received data packet
uint8 m_data_type; //The type of the received data packet
}data_record;

Conclusion
This system comprehensively uses GPS satellite positioning technology and GPRS wireless network transmission technology, and combines the two for vehicle navigation and monitoring and dispatching.
This system can be applied to various types of operating vehicles, and it has now been applied to two-person unpowered sightseeing vehicles with good results.

References
1 Trimble Company, Lassen SQ GPS Receiver System Designer Reference Manual[M], Revision A, US: June 2002
2 Jean-Lien C. Wu, Wei-Yeh Chen, Hung-Huan Liu, Radio Resource Allocation in GSM/GPRS Networks, Lecture Notes in Computer Science, Volume 2343 / 2002, January 2002, Pages: 457-468