LI Ze-ming(李泽明), LI Jin-ming(李锦明)，YANG Yan-jiao(杨燕姣)

(Department of Electronic Science and Technology, North University of China, Taiyuan 030051, China)

Remote positioning system based on GPS/GPRS*

LI Ze-ming(李泽明), LI Jin-ming(李锦明)，YANG Yan-jiao(杨燕姣)

(Department of Electronic Science and Technology, North University of China, Taiyuan 030051, China)

Considering the need of target positioning, a remote positioning system is designed based on global positioning system (GPS) and general packet radio service(GPRS); The data collection terminal is based on microcontroller unit (MCU) PIC24FV301. It uses GPRS network to create wireless link and transmits GPS source information which is collected by LEA-5H board to monitor center on the Internet．The monitor center obtains the target information through processing and analysis of the calculated data. Actual operation results indicate that the designed system has excellent performance and achieves the goal of the remote location.

global positioning system (GPS); general packet radio service(GPRS); microcontroller unit (MCU); remote target positioning

Global positioning system (GPS) is developed based on satellite positioning technology. It provides users with positioning, navigation and timing (PNT) services. The free, open and dependable nature of GPS has led to the development of hundreds of applications affecting every aspect of modern life, including agriculture, aviation, space, enviroment, marine, public safety and disaster relief, etc[1-4].

General packet radio service (GPRS) is a packet-switching technology that enables data to be transferred through cellular networks. It is developed based on globle system for mobile communications (GSM). GPRS can be used for mobile Internet, multimedia messaging service (MMS) and other data communications.

This paper presents a remote positioning system based on GPS and GPRS technologies. On the one hand, it is able to provide high-precision positioning data, which is substantially independent of time or geographical constraints; On the other hand, GPRS network coverage is extensive and has a high reliability, which provides efficient and economic means of remote wireless data transmission for remote positioning terminal.

1 System description

1.1 Structure of remote positioning system

Remote positioning system mainly consists of positioning terminal and GPS satellite, general packet radio service/global system for mobile communications(GPRS/GSM) network and monitoring center. The system diagram is shown in Fig.1.

Fig.1 Remote positioning system

The main role of the positioning terminal is to receive back positioning data from GPS receiver module, and then transmit it to GPRS communication module after processed by the microcontroller. By connecting the positioning erminal with the monitor center through GPRS network, real-time transmission of the positioning data to the monitor center is achieved.

1.2 Hardware design

The positioning terminal unit is constituted by a microcontroller unit (MCU), a GPS receiver module, a GPRS module, a power supply module, a SIM card, GPS antenna and interface modules and status lights， and so on.

The block diagram of positioning terminal unit is shown in Fig.2.

Fig.2 Positioning terminal unit

1.2.1 Microcontroller unit design

The positioning terminal unit uses PIC24FV301[5]of Microchip as microcontroller.

Fig.3 Serial circuit diagram

The microcontroller has wide operating voltage range of 2 V-5.5 V and standard watchdog timer

has wake-up function for Sleep/Deep sleep with ultra-low power consumption. Two serial data transfer ports are connected with GPS and GPRS modules. Serial connection diagram is shown in Fig.3.

1.2.2 GPS satellite positioning module

LEA-5H GPS satellite positioning module is chosen as remote positioning terminal module[6]. It internally integrates the world's most advanced GPS engine and supports both GPS and Galileo positioning platforms. The number of the GPS channels increases from 16 channels of the fourth generation to 50 channels of the fifth generation.

The peripheral circuit of the GPS module is connected as shown in Fig.4.

Fig.4 Interface circuit of GPS module

1.2.3 GPRS wireless communication module

GPRS wireless communication module of the remote positioning terminal is SIM900 from SIMCom, which is a quad band GSM/GPRS module[7]and working bands are EGSM 900 MHz and DCS 1 800 MHz. The SIM900 module provides a fully functional system interface and also provides AT command interface. These advantages enables it to be integrated into their own applications within a short period of time.

The peripheral circuit diagram of SIM900 module is shown in Fig.5.

Fig.5 Peripheral circuit diagram of SIM900

2 Software design

2.1 Controller software design

The flow chart of controller software design is shown in Fig.6.

Fig.6 Flow chart of microcontroller

Once power is switched on, the positioning system is reset. Then the MCU is initialized and Watchdog overflow time is set[8]. Eventually MCU goes into sleep mode. When the Watchdog arrives at the overflow time, the microcontroller is woken up from sleep mode. Judging R13 output level is low or high, if it is low, MCU enters the sleep mode repeatedly; If it is high, MCU enters normal operating mode. Positioning terminal unit will send location information to the monitor center through GPRS circularly.

2.2 GPS receiver module software design

2.2.1 Data format

GPS data begins with “$”[9], and subsequently the other satellite information emerges with comma as separator, and a carriage return-line feed pair as end marker. Usually there are six kinds of GPS data formats. This paper selects character string “$ GPRMC” to extract the location information. The format is as follows:

“$ GPRMC, 135,704.00, A, 3 800.820 41, N, 11 226.549 70, E, 1.81, 15.00, 070 312… ”.

The following location information will be extracted from the system.

1) Satellite positioning time: “135,704.000”, which refers to a positioning time of 04.000 s at 13:57. It is translated into Beijing time as 13+8=21:57:04 s.

2) Satellite positioning status:“A”. It indicates that the valid data is received.

3) Latitude: 3 800.820 41. It refers to the latitude 38°, 0.820 41′, and it can be converted to 38.013 673 5°.

4) Latitude distinction: “N” refers to northern hemisphere.

5) Longitude: “11 226.549 70” refers to the longitude 112°, 26.549 70′, being 112.442 495° after conversion.

6) Longitude indicator: “E” for east longitude.

7) Positioning date: “070 312” indicates that positioning date is March 7, 2012.

2.2.2 GPS data extraction

The serial port1 of PIC24FV32K301 communicates with GPS receiver module through serial connection. The GPS data is output in the form of data stream.

The flow chart of GPS module data extraction flow is shown in Fig.7.

Fig.7 Flow chart of GPS data processing program

2.3 GPRS module software design

Attention[10], the AT instruction, is transmitted from the terminal equipment to the data circuit terminal equipment. By sending AT commands to control the GPRS module of the positioning terminal, the interaction of the positioning terminal and GPRS network is achieved. SIM900 module is controlled via AT commands, and the microcontroller sends control instructions to SIM900 through the serial port 1.

The AT control commands of positioning terminal transfer data to the monitoring center, as shown in Table 1.

Table 1 AT commands of GPRS data transition

Flow chart of the GPRS module data transmission is shown in Fig.8.

Fig.8 Data transmission flow chart of GPRS module

3 Results

After the completion of the system development, we test the positioning terminal under the gravel. At the initial stage the data received by the monitoring centre continuously changes. When the received data becames stabilie, the error value between the actual position data of the positioning terminal and the positioning data is determined. Experimental results are shown in Table 2. Comparing the experiment data, it can be found the location information hardly changes at 18∶20∶06, and afterward the data from the satellite searching is in the stabilization. When the effective latitude and longitude data are put into the Google earth, the error between the measured position and true position is obtained, as shown in Fig.9.

Table 2 Experimental results

It can be seen that the distance between the location information received by the monitor center and the actual position of the positioning terminal is 6.66 m. This error range is consistent with that from the indicator of the positioning system.

Fig.9 GPS positioning information

4 Conclusion

This paper designs a remote positioning system based on GPS/GPRS, which is a fusion of computer technology, satellite positioning technology and modern communication technology for remote positioning. The designed positioning terminal can accurately obtain positioning data and implement remote wireless data transmission using GPRS technology. It has a good prospect and practical value.

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date： 2013-01-15

LI Ze-ming (lizeming565@163.com)

CLD number： TN927+.23 Document code： A

1674-8042(2013)03-0276-06

10.3969/j.issn.1674-8042.2013.03.016