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568 IEEE Transactions on Consumer Electronics, Vol. 54, No. 2, MAY 2008 (7) Information security method. In order to ensure the PSoC device which reduces the design complexity of security of system information, some security methods capacitive sensor keyboard in the system. are taken, such as a password for gateway to prevent The wireless data transfer between gateway and sensor unauthorized person to access the system, and a pseudo nodes is implemented with a wireless transceiver module. The security key for data encryption and decryption to module operates in the unlicensed worldwide 2.4GHz ISM ensure security wireless communication. (Industrial, Scientific and Medical) band and has many The paper is organized as follows. Section II presents the excellent features: (1) low power consumption, 21mAgeneral structure of the proposed system, as well as its main operating current and sleep current less than 1μA; (2) DSSSfeatures and components. Section III shows the design of (Direct Sequence Spread Spectrum) data rates up to 250kbps,GSM/GPRS gateway and Section IV shows the design of GFSK (Gaussian Frequency Shift Keying) data rate of 1 Mbps;security sensor nodes. Section V discusses the communication (3) Operating range is 10m plus; (4) 4 MHz SPI (Serialbetween the gateway and the security sensor nodes. In Section Peripheral Interface) microcontroller interface.VI, the preliminary experimental functions of the system areshown and, finally, in Section VII, conclusions are presented, III. THE GSM/GPRS GATEWAYreferring perspectives for future work. A. Hardware of GSM/GPRS Gateway II. THE HOME SECURITY SYSTEM The diagram of the hardware of GSM/GPRS gateway is shown in Fig. 2. The GSM/GPRS gateway contains six major The general structure of the home security system is shown components:in Fig. 1. The system includes two parts: wireless security (1) Microprocessors, including I and II;sensor nodes and a GSM/GPRS gateway. There are three kinds (2) Wireless transceiver module;of sensor nodes in this system: door security nodes, infrared (3) LCD;security nodes and fire alarm nodes. The GSM/GPRS module (4) LEDs (Light Emitting Diodes) and a buzzer;is the interface between the gateway and the GSM/GPRS (5) Capacitive sensor keyboard;network. (6) GSM/GPRS module. GSM/GPRS gateway UART interface SMS Security nodes GSM/GPRS module The mobile phone of remote user Fig. 2. The diagram of GSM/GPRS gateway Fig. 1. The structure of home security system Microprocessor I is the central device of the gateway. It The microprocessor used in this system is 8-bit PSoC receives the information coming from nodes and sends out(Programmable System on Chip) device. There are three alarm messages to remote users via GSM/GPRS module.reasons to use this device. Firstly, it makes the design easier Microprocessor II deals with the keys’ signals and sends theand reduces system cost. It has configurable analog and digital signals to microprocessor I through its SPI interface.blocks, as well as programmable interconnects logic. This In this system, the communications between the GSM/GPRSarchitecture allows users to create customized peripherals such module and Microprocessor I are implemented in the form ofas filters, amplifiers, analog to digital converters, AT (Attention) commands.communication interfaces and so on. Secondly, this device has The implementation of GSM/GPRS gateway is shown in Fig.a sleep timer and SMP (Switch Mode Pump) circuit, which are 3.useful to reduce power consumption. Thirdly, there is a special
Y. Zhao and Z. Ye: A Low Cost GSM/GPRS Based Wireless Home Security System 569 Fig. 3. The implementation of GSM/GPRS gatewayB. Software Design of GSM/GPRS gateway The working procedure of gateway is as follows: (1) The wireless transceiver module receives the states information of security sensor nodes and sends the Fig. 4. The flowchart of main program of microprocessor I information to microprocessor II through its SPI interface. Fig. 5 shows the flowchart of the menu subprogram. (2) LCD displays the information of sensor nodes. When (1) Check up password. alarm incidents happen, LCD will display alarm (2) If the password is right, the menu appears on LCD, information. LEDs and the buzzer will warn the users at otherwise the sub program ends at once. home. At the same time, the gateway will send alarm (3) Press 1 to 4 corresponds to the four functions of the SMS messages to remote PMP and users through the menu: 1 for initializing password and the SOS number, GSM/GPRS module. 2 for changing password, 3 for changing the SOS (3) Sixteen capacitive sensor keys including an emergency number and 4 for quit. These functions are discussed in alarm key (SOS key) are designed to modify password Section IV in detail. and mobile phone number for receiving the alarm messages. What’s more, the SOS key is used to startup emergency alarm. The function of microprocessor II is receiving keyboard’sinformation and sending it to microprocessor I through SPIinterface. Its procedure workflow is to scan keyboard in turnsand to send out signals corresponding to the keys which aretouched by fingers of user. The flowchart of main program of microprocessor I isshown in Fig. 4. (1) Initializes system. (2) Receives information of sensor nodes and keyboard. (3) If any node alarms, the program calls alarm subprogram to display alarm message on the LCD and sends corresponding SMS messages to remote PMP and users. (4) If user at home presses the SOS key, it means he/she wants to alarm immediately. Then, the system will send the SOS message to remote PMP and users at once. (5) If user wants to use the menu function of gateway, he/she need to press the Menu key. Then, the program calls menu subprogram. Fig. 5. The flowchart of menu subprogram
570 IEEE Transactions on Consumer Electronics, Vol. 54, No. 2, MAY 2008 IV. WIRELESS SECURITY SENSOR NODESA. The General Structure of the Sensor Nodes The general diagram of wireless security sensor nodes isshown in Fig. 6. Every sensor node has a wireless transceivermodule and a microprocessor. The microprocessor receivesand analyses the sensors’ signals to detect the state of node. Fig. 8. The implementation of a door security node C. The Infrared Security Node The infrared security node adopts a pyroelectric infrared Fig. 6. The general diagram of nodes sensor (PIR). PIR sensor responds to the infrared radiation of human body whose radiation is strongest at wavelength Two methods are taken to reduce power consumption of between 9.4 μm and 10.4 μm . The sensor can be placed innodes: the entrances of rooms or other areas. When an intruder enters (1) SMP circuit. It can be used to generate typical operating these areas, the sensor will detect the infrared radiation supply voltages off a single battery using only a few generated by the intruder and output a signal whose range is external components. As long as external voltage is about 1mV and frequency is about 1Hz, as shown in Fig. 9. more than one volt, the microprocessor would work normally, so the node can work steadily for a long time. (2) By configuring the sleep timer, the microprocessor can go into sleep mode periodically, which reduces average power consumption.B. The Door Security Node Door security node adopts magnetic sensor. The sensordoesn’t need external power supply and has an ON/OFF signaloutput according to the distance from magnet to dry spring.The distance threshold is 16 mm. As the sensor is normally inON state, the circuit in Fig. 7 is designed to use a 1MΩresistor R1 to limit the circuit current so as to reduce powerconsumption. The implementation of a door security node isshown in Fig. 8. VCC Fig. 9. Output signal of PIR sensor Magnetic sensor Since the output signal of PIR sensor is very small, signal R2 processing circuit must be designed. The common method is Micro- using a special amplifier to process the signal . The circuit 330 processor has a stable output and a quick response. However, it is R1 complex, high power consumption and high cost. 1M Since microprocessor contains configurable analog and digital blocks which can be configured as filters, amplifiers and analog to digital converters, the other simpler method is to use these configured filter, amplifier and ADC (Analog to Digital Converter) to process the signal, as shown in Fig.10. Fig. 7. Circuit of door security node The output signal of PIR sensor is wired to microprocessor
Y. Zhao and Z. Ye: A Low Cost GSM/GPRS Based Wireless Home Security System 571after a RC (resistor-capacitor) filter. The signal processesinside the microprocessor include amplifying, further filtering,analog to digital conversion and comparing with the alarmthreshold determined by experiments. This method greatlysimplifies circuit and reduces the power consumption. The implementation of infrared security node is shown inFig. 11. VCC Fig. 12. The implementation of a fire alarm node 6.8M V. THE WIRELESS COMMUNICATION When alarm incidents occur, the nodes will send alarm information to the GSM/GPRS gateway immediately. If there 47u is no alarm incident, the gateway and sensor nodes use a query-reply communication mode. When a node is queried, it 6.8M 0.01u 20K returns its state to the gateway. The communication packet format between the gateway and node is given in Fig. 13. The packet consists of Preamble (P), Start of Packet (SOP), Packet Length (PL), Payload Data (PD) and the CRC16 bits. Fig. 10. Circuit of PIR sensor with a RC filter Payload data have two bytes. The first byte represents the identity of security node, the second byte represents the state of node (0x00000001: “Open” State; 0x00000010: “Close” State; 0x00000100: “Alarm” State) or query command (0x00001111) from gateway. Before the payload data is transferred, it is encrypted with a pseudo security key. The payload data is decrypted with the same pseudo security key after received. The security key is generated by GSM/GPRS gateway and is sent to each node when installing. Fig. 13. The communication packet format Fig. 11. The implementation of an infrared security node VI. THE SYSTEM FUNCTION A. Alarm FunctionD. The Fire Alarm Node The home security system discussed above has two kinds There are many fire-detection techniques. The common of alarms: abnormal alarms issued from three sensor nodes andmethods are based on temperature sampling, relative humidity emergency alarm started by users when they touch “SOS” key.sampling, smoke analysis, in addition to ultraviolet and Table I presents messages on LCD and SMS messages sent toinfrared sampling.  presents a fire-alarming method based user when alarms take place.on video process. Although the method mentioned in  can TABLE Iprovide additional information about the process of burning, it ALARM FUNCTIONS OF SYSTEMis too expensive to be used in home security system. In this system, each fire alarm node adopts a temperature Alarm Type LCD SMSsensor and an infrared receiver. The temperature sensor door security nodes’ alarm Door Alarm Door Alarmmonitors environment temperature and infrared receiver MESSAGE SENTmonitors heat and flames. If temperature or infrared of infrared security nodes’ alarm Stealing Alarm Stealing MESSAGE SENT Alarmenvironment exceed defined thresholds, the node sends out fire alarm Fire Alarm Fire Alarmalarm signal. The implementation of a fire alarm node is MEDSSAGEshown in Fig. 12. It is simple design, low cost and suitable to SENTuse in home. emergency alarm SOS!!! HELP!!! MESSAGE SENT
572 IEEE Transactions on Consumer Electronics, Vol. 54, No. 2, MAY 2008B The Menu Function  J. A. Gutierrez, M. Naeve, E. Callaway, M. Bourgeois, V. Mitter, and B. Heile, “IEEE 802.15.4: a developing standard for low-power low-cost “Menu” key should be touched in order to use functions of wireless personal area networks,” IEEE Network, vol. 15, no. 5, pp. 12-menu. User is requested to enter password firstly. If the input 19, Sept-Oct. 2001.password is correct, the system menu will show on the LCD.  Y. P. Tsou, J. W. Hsieh, C. T. Lin, and C. Y. Chen, “Buliding a remote supervisory control network system for smart home applications,” IEEE (1) Initialization International Conf. on System, Man and Cybernetics, pp. 1826-1830, Press “1”, the system password is changed to “222333” Oct. 2006. and mobile phone number for help is changed to  L. Ophir, “802.11 Over Coax – A Hybrid Coax – Wireless Home “00000000000”. Network Using 802.11 Technology,” Consumer Communications and Networking Conference, pp. 13-18, Jan. 2004. (2) Change password  H. S. Kim, and C. G. Lee, “Wireless USB based home security system Press “2”, the system requests user to enter new on the OSGi service platform,” International conf. on Consumer password. When completed, the system asks user to Electron., pp. 1-2, Jan. 2007.  B. Yusekkaya, A. A. Kayalar, M. B. Tosun, M. K. Ozcan, and A. Z. input again to verify. If two inputs are same, the Alkar, “A GSM, internet and speech controlled wireless interactive password will be changed to the new one. During the home automation system,” IEEE Trans. Consumer Electron., vol. 52, process, you can use “Cancel” key to delete what you no. 3, pp. 837-843, Aug. 2006.  A. Alheraish, “Design and implementation of home automation have entered. system,” IEEE Trans. Consumer Electron., vol. 50, no. 4, pp. 1087- (3) Change mobile number 1092, Nov. 2004. Press “3”, the system displays the existing mobile  S. Lee, K. N. Ha, and K. C. Lee, “A pyroelectric infrared sensor-based number and prompts user to enter new number. When indoor location-aware system for the smart home,” IEEE Trans. Consumer Electron., vol. 52, no. 4, pp. 1311-1317, Nov. 2006. finish inputting mobile phone number, press “Set” key to  B. Li, B. Jiang, and B.Q. Wang, “Application of BISS0001 on heat- complete the amendment. released infrared switch,” Application Science and Technology, vol. 33, (4) Quit no. 2, pp. 31-33, Feb. 2006.  P. H. Huang, J. Y. Su, Z. M. Lu, J. S. Pan, “A fire-alarming method Press “4”, the system quits the menu. based on video processing,” Intelligent Conf. on Intelligent Information Hiding and Multimedia Signal Processing, pp. 359-364, Dec. 2006. VII. CONCLUSION This paper presents the design and the implementation of a Yanbo Zhao was born in Shijiazhuang, China on July 18,wireless home security system. PSoC devices and wireless 1984. He received the B.S degree from Harbin Institute oftransceiver modules are adopted. The system has a friendly Technology, Harbin, China, in 2006. He is currently pursuing his M.S degree at Tsinghua University, Beijing,user interface and employs some methods to reduce the power China. His main research interests are home automationconsumption. network, home network security and electronic Communication of the system is complete wireless, which technology applications.makes the system easy to install and use. The system is low Zhaohui Ye was born in Hunan Province, China oncost, low power consumption and easily operable. In addition, December 14, 1968. She received her B.S, M.S., andthe wireless transceiver modules enable the system to transfer PHOTO Ph.D degrees in Industry Automation Instrument, Reactor Engineering and Reactor Security, and Control Scienceother information such as voice and picture rather than just and Engineering from Tsinghua University, Beijing,alarm signals. As a result, the system can lightly be expanded China, in 1992, 1994, and 2004, respectively. She hasto other applications. been working in Automation Department at Tsinghua The system is secured with a login password. As a future University, Beijing, China since 1994, and now she is an associate professor. From September, 2002 to March, 2003, she studied as awork, we are currently working to establish a more secure Visiting Scholar in Extension and Teaching Development Center atsystem by researching a proper wireless security protocol. University of California, at San Diego, USA. Her main research interests are home automation network, electronic technology application, and analog integrated circuit design. ACKNOWLEDGMENT The author would like to thank Lucan Lin, Xiaolong Chenfor their contribution to the design and implementation of thesystem. REFERENCES K. C. Lee, “Network-based fire-detection system via controller area network for smart home automation,” IEEE Trans. Consumer Electron., vol. 50, no. 4, pp. 1093-1100, Nov. 2004. A. Z. Alkar, “An internet based wireless home automation system for multifunctional devices,” IEEE Trans. Consumer Electron., vol. 51, no. 4, pp. 1169-1174, Nov. 2005. Y. Tajika, T. Saito K. Termoto, N. Oosaka and M. Isshiki, “Networked home appliance system using bluetooth technology integrating appliance control/monitoring with internet service,” IEEE Trans. Consumer Electron., vol. 49, no. 4, pp. 1043-1048, Nov. 2003.