Research on the Architecture of Vehicle Positioning and Anti-theft System Based on DSP Technology

Overview

With the improvement of people's living standards, cars have gradually entered families, and the requirements for car anti-theft are getting higher and higher. Although the car anti-theft devices on the market are gradually improving, these anti-theft devices mainly use call alarms, high-voltage electric shocks, etc. With the development of science and technology, car theft technology is getting more and more advanced, making it difficult to prevent. Car anti-theft has extremely important research value for both car manufacturers and social insurance industries. In response to the current upward trend of car thefts worldwide, various car manufacturers are constantly improving anti-theft technology, especially with the advancement of microelectronics technology, car anti-theft technology has developed towards automation and intelligence.

Since the GPS system was officially built and put into use in the United States at the end of the last century, GPS technology has penetrated into all areas of human economic development. The GPS market is currently quite large, especially in the field of vehicle positioning and navigation, which has the largest market share and the fastest growth. Recent statistics show that the sales of vehicle navigation systems equipped with GPS receivers in 2000 increased from US$500 million in 1996 to US$3 billion, and this trend will continue. Under the temptation of this market, countries around the world have launched a lot of research on vehicle navigation and positioning technology. At present, my country's automobile GPS positioning and navigation is still in its infancy, and GPS navigation equipment and application systems for special vehicles have begun to be launched. For example, relevant departments have adopted GPS to monitor the entire process, guide and command special vehicles such as cash transport vehicles, ambulances, buses, patrol cars, welcoming cars, prisoner cars, etc.

GSM format is the main format used in mobile phones at present, accounting for more than 80% of the market share. Combining GPS with GSM can not only use GPS technology to perform global positioning of the car and achieve good navigation, but also use the wide coverage area and SMS function of the GSM network to enable car owners to have timely understanding of the current status of the car, thereby improving the overall navigation and anti-theft performance of the car.

1 System architecture design

The structural block diagram of the automobile positioning and anti-theft function system based on DSP chip, which consists of GPS module, GSM wireless communication module and necessary auxiliary circuits, is shown in Figure 1. In Figure 1, DSP controls both GPS and GSM modules through serial ports. The GSM module is connected to the serial port of DSP itself, and 8251 is used to expand a serial port for GPS module. The detection control and its auxiliary circuits can directly use the I/O port of DSP. The I/O ports of TMS320LF240 DSP chip have multiplexing functions, so you only need to set information in the control register to make the I/O as general I/O.

After the system with DSP as the controller is started and initialized, it will be in a state of constantly receiving the car's position information. At the same time, the system is also waiting for the interruption of detecting the status and receiving the user's query message. Once an interrupt occurs, it will transfer to the corresponding interrupt processing subroutine. If the system's defense signal is invalid, the control system will not perform the above operations.

After the system's defense signal is effective, the DSP mainly processes the location information received by the GPS receiver in a loop. Every time a new message mark is obtained, the subroutine is called to process the message, mainly to separate useful information in the message such as latitude and longitude, time and checksum, and store these data in the specified storage space. The wireless communication module TC35T also exchanges information with the DSP through the serial port. In this case, the serial port reception uses interrupts to obtain the right to use the controller. If an abnormal vehicle condition occurs, such as the door opening and engine starting in the defense condition, an interrupt request will also be sent to the DSP. In the software, the interrupt caused by TC35T is set to a low priority, that is, if the vehicle condition is abnormal and the owner actively queries the message, the DSP controller will not respond to the interrupt request of TC35T.

If the DSP controller receives an interrupt request and determines that the interrupt is caused by the engine start signal (it can be delayed for a certain period of time, such as 100 ms, and then detected again. If it is still valid, it is determined that the start signal is valid, which can prevent misoperation). The system will process the engine start interrupt service subroutine and send a short message (the engine is running) to the user (the number of times it is sent can also be set). If the owner does not respond in time, it can be sent again after 5 minutes, and the local alarm signal can be sent at an interval of 1 minute, and each time it lasts for 30 seconds; the power off and oil off signals are immediately effective (in this simulation experiment, two indicator lights are on), and the brake signal is also effective after 20 seconds; at the same time, the processing results and the current location information received by the GPS receiver are sent to the owner through wireless communication. Similarly, if the signal of the left door or right door being damaged or vibrating is detected, the processing method is similar except that the content of the short message sent to the owner is different.

When the user's mobile phone sends a check status short message to request the control system to return the current status, the control system will respond differently according to the current system status: when it is not in the armed state, the control system will send a short message of "defen ses isnt it set" to the user; when it is in the armed state, if the system is intact, it will send a short message of "all is ok" to the user. If the system has been damaged, the corresponding treatment measures have generally been taken, such as locking the engine first, then the engine will be sent to the user at this time, and the further treatment method will be sent to the user at the same time. To unlock, the user needs to send a certain password and send an unlock engine message to the control system to effectively unlock. Other situations are handled in a similar way.

2 System feasibility analysis

2.1 DSP Technology

DSP has extremely high-speed digital processing capabilities and a large amount of computing power. Therefore, it can meet the requirements of efficient real-time signal processing. The characteristics of this new device are as follows:

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(1) Adopting the Harvard architecture, highly parallel computing greatly improves the computing speed;

(2) The chip is equipped with one or more hardware multipliers and accumulators, which can implement single-instruction multiplication, addition and address-modification operations;

(3) The chip is equipped with powerful special instructions that can realize overlapping operation of instructions;

(4) The chip is equipped with a variety of powerful peripheral devices and interfaces, making its computing speed many times faster than that of a PC;

(5) DSP adds hardware loop control. After loop initialization is completed, the loop no longer consumes instruction cycles in actual operation. This greatly improves the speed of digital signal processing.

(6) DSP has low cost and its sales price decreases year by year.

In the DSP field, Texas Instruments (TI) products and their supporting technologies and development tools are currently widely used in the market. The TMS320LF240 used in this article is one of the TMS320C24x series. TMS320LF24x, also known as DSP controller, is a cost-effective 16-bit fixed-point DSPs launched by TI in 1997. It is specially designed for the control of motors, inverters, robots, CNC machine tools, etc.

Since the current research is still in the simulation stage, the signal for detecting the vehicle condition is triggered by a switch, and the reaction to the vehicle condition signal is determined by whether the indicator light is on, so the circuit outside the board is relatively simple. The DSP controller controls the GPS receiving module and the wireless communication module GSM through the serial port, and TMS320LF240 has only one serial port, so the serial port needs to be expanded. In addition, the monitoring status is triggered by interrupts to trigger the DSP control function. TMS320LF240 has only three external maskable interrupt sources, so the external interrupt also needs to be expanded. Other used ports can be set as general I/O ports.

2.2 GPS Basic Principles

The United States began to build the global positioning system GPS in 1973 and put it into full use in 1994. The global positioning system (GPS) consists of three sections: GPS satellite constellation, ground control/monitoring network and user receiving equipment. Among them, the user equipment is mainly a satellite signal receiver, which has different positioning capabilities according to different purposes. The basic function is to receive the L1 carrier, separate the C/A code, and perform the simplest virtual distance positioning. It is also the model used for general vehicle positioning. It must be noted that: GPS satellites generate two different carriers to carry all codes and messages. Among them, the C/A code is only set on the L1 carrier, and the P code is set on the L1 and L2 carriers respectively, and is distinguished as P1 and P2 codes. The functional block diagram of the GPS receiving module used by general users is shown in Figure 2. It is mainly composed of frequency receiving processing circuit and signal processor. Now, in order to save certain recent location information, program memory and data memory are added at the same time. Among them, the I/O interface includes serial port and general data port, which are directly used by users.

2.3GSM Short Message Service

The GSM system can provide two major services, namely basic services and supplementary services. Basic services include telecommunication services and bearer services; supplementary services are not provided separately, but are a supplement to basic services. The telecommunication services provided by GSM include telephone, short message and fax. Short message service is the only service in the GSM system that does not require the establishment of an end-to-end service path. Even if the mobile station is in a completely circuit communication situation, short message transmission can be carried out, that is, the transmission of a message constitutes a communication.

The TC35T wireless GSM communication terminal used is a wireless module TC35 integrated with necessary interfaces by Siemens. The TC35T module is used as a sending and receiving device, and the transmission of short messages is used to realize the exchange of information about the car's location and monitoring and control between the car owner and the on-board control. This method has the advantages of low communication cost, high spectrum utilization, large system capacity, multiple business types, good confidentiality, strong anti-interference ability, high call quality, automatic roaming, etc. It uses signaling channels for transmission, does not need to dial to establish a connection, and directly sends the information to be sent with the destination address to the short message service center, which then sends it to the final destination. It is currently a widely used communication solution. 

3 Conclusion

This article combines the car positioning and anti-theft functions into consideration, so there will be no duplication in the installation of equipment. At the same time, it also raises anti-theft and positioning to the level of intelligence, and also lays the foundation for networking development. Using DSP and TMS320LF240 series as controllers has many advantages that other controllers do not have.