Abstract—Smart home is one of the cutting-edge technologies in today’s international intelligent building field. The smart home system has been used to adopt complex integrated wiring technology to achieve information interaction. There are several disadvantages identified with this method, for example, it needs to design in advance, layout techniques is difficult, wiring is cumbersome and so on. We propose a hybrid network programs, which combines ZigBee-based wireless sensor networks with power line carrier network. The system not only avoids cabling but also greatly enhances the system’s scalability and robustness.

I. INTRODUCTION

MART home is of great importance in the intelligent life nowadays. It can help people live more efficiently,

conveniently and comfortably. With the advent of the information age, as well as computers, mobile phones and other modern communication devices have been widely used, making a new generation of smart home for us. In a new generation of smart home, people’s lives have brought to an unprecedented convenience. For example, it allows people to control the intelligent device while working outside, by just clicking the phone lightly. The smart home can also allow people to turn on the air-conditioning, heat the bath water before returning home. It also can detect the indoor gas concentrations, determine whether there is a gas leak; check water and electricity usage; achieve the water, gas and meter remote reading. When theft or potential security risks are encountered, the system will automatically alarm, notify the user to take some appropriate response measures.

II. SYSTEM ARCHITECTURE

A. System Structure Smart home or the intelligent building is moving to wireless remote control, multimedia control, high-speed data transmission and other directions. The key of this system is to have a family controller with strong compatibility and can also meet the needs of home network information transmission [1-3]. At present, integrated wiring technology is used in most of the transport networks [4], which not only limits the application occasion of the system, but also is very expensive. Using wireless mode to build a flexible and convenient smart home security monitoring system becomes a research hotspot. At present, smart home applications of

F. A. Tao Hu is a graduate student major in computer application technology, Ningbo University, Ningbo, China (phone: 0574-87600828; fax: 0574-87600351; e-mail: hutao_841129@ yahoo.com.cn).

S. B. Ding Zhang is a graduate student major in circuit and system, Ningbo University, Ningbo, China (e-mail: zhangding19561122@163.com).

T. C. Shuang-dong Zhu is a professor of Information Science and Engineering College, Ningbo University, Ningbo, China (e-mail: zhushuangdong@nbu.edu.cn).

wireless communication technology include: Infrared technology, Bluetooth technology and ZigBee technology [5]. Infrared technology refers to a short-range, half-duplex, point to point communication. Because of its high error rate, it cannot be used in the home networking. Due to the limited network capacity and expensive cost，Bluetooth technology is not suitable for more home node network application. This paper utilizes ZigBee technology which has moderate transmission distance, high security, and larger network capacity [6] to build network. Taking into account that ZigBee does not have the characteristics of penetrating walls [7], and each room of the ZigBee wireless network is a separate network, and wireless networks cannot carry out information exchange effectively. Therefore this paper presents a hybrid network design that combines ZigBee-based wireless sensor networks and power line carrier network (block diagram shown in figure1).

That means in each room adopts ZigBee wireless networking to achieve terminal equipment and the ZigBee coordinator node interacts information through wireless means within the family, different rooms of the coordinator nodes and intelligent home control platforms using power line carrier communication technology to communicate, so that full use of the power line that has been laid completely within the family to reduce costs. Consequently, achieve seamless link between terminal equipment and control platform for information exchange, greatly enhanced system reliability and stability. In addition, control platform modules through GSM module to communicate with the user, when any risk occurs within the family, send SMS to notify the user immediately. Moreover, mobile phone users can also use the terminal to control and operate the corresponding family devices.

B. ZigBee Network Topology Selection ZigBee is a short-range, low-power, low-cost bidirectional wireless communications technology, mainly applied to the field of automatic control and remote control. IEEE802.15.4

A Hybrid Sensor Network in the Application Design of Smart Home Tao Hu, Ding Zhang, and Shuang-dong Zhu

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Fig. 1. This is the system structure diagram, which shown that the whole system is consisted of wireless communication section and cable communication section. Coordinator and the terminal communicate with each other using wireless mode in each room. Coordinators in different rooms using cable mode realize communication.

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Third International Workshop on Advanced Computational Intelligence August 25-27, 2010 - Suzhou, Jiangsu, China

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is the basis for ZigBee technology [8], and compared to high-speed personal area networks, Bluetooth and 802.11x wireless local area network, ZigBee protocol is simpler and more practical. This article will use TI’s low-power, on-chip system-on-chip production ZigBee CC2430. There are three kinds of ZigBee network topology [9]: star, tree cluster-type and mesh networks. Mesh network has high fault-tolerance ability, good adaptive capacity, far transmission distance, but its complexity is high; Star Network is of simple and low-power consumption features, easy to use, and suitable for small-scale, low-complexity occasions. Tree cluster-type is found between the two. Since each room is a separate wireless network, the network size is small, and the distance is short. Considering low-power performance, this paper adopts star topology for wireless networking.

C. P LC Chip Selection Power line carrier (hereinafter referred to as PLC) communication refers to using the existing power line, by means of carrier technology to transport analog or digital signal information. Its greatest feature is in a distribution transformer region it does not need to re-erect network [10], and can transfer data as long as power lines can reach. The way that room coordinator nodes and the smart home control platform communicate with each other using the power line will solve the issue of multi-wall effectively. This paper uses the PLC chip PL3105, which is an autonomous research and development of our country’s PLC chip [11]. It is a System on Chip which is designed for automatic meter reading, intelligent information application, and remote monitoring. It uses 805l instruction-compatible high-speed microprocessors; embedded carrier communication unit to realize remote communication in the low-voltage power line networking. By means of configuration registers, CPU can achieve right control of the carrier communication, interface is convenient; spread spectrum communication unit with the strong ability of anti-band frequency interference and the advantages of high sensitivity. It also integrates a perfect power-on voltage monitoring and a power-down reset watchdog circuit to ensure the run-time reliability of the system.

III. SYSTEM HARDWARE DESIGN

A. ZigBee Wireless Communication Module This part of the design as shown in figure 2 mainly consists of data collection section, wireless transceiver part, power management and control unit circuit.

Data acquisition consists of: CC2430, functional sensors (such as smoke, CO concentration, flame, infrared, temperature and humidity sensors, etc.) and power supply circuit three parts, realizes real-time collecting of environment-related information within the home. Wireless transceiver module is made up of ZigBee coordinator node (from as the CC2430), CC2430 and power management circuitry. In order to improve the reliability of the system, the power management circuit of this part uses automatic switching dual-supply power mode that is in the normal situation no-load low-power AC-DC circuit to supply power, while the power outage, the circuitry automatically switches to battery power supply mode. After city electrical power system restores the system automatically switches to the AC-DC power supply mode. At the same time, battery power measurement circuit is designed for this part, when the battery is low, it gets through wireless transceiver part sending the information to coordinator node, then the PLC module sends back to the home control platform, it finally gets through the GSM module send to notify the user to replace a new one, further enhance the system’s reliability. In addition, the power management and control unit circuits of this part can also be used to control corresponding terminals (for example, by controlling the relay to control the air conditioning off or on, etc.), LCD-screen display (for display address number of the terminal device)and so on. Finally, each room coordinator node gets through the PLC communication module to communicate with intelligent control platform.

B. PLC Communication Module As direct-sequence spread spectrum modulation circuit required by PLC communication has been integrated in the PL3105 chip [12], in sending state, PL3105 automatically passes the data to a series of processing: such as encoded, spread spectrum, modulation and so on. After that, the chip outputs carrier spread spectrum with center frequency of 120 kHz, then the carrier signal amplified by the power amplifier, through the coupling circuit coupled to the power line to complete the sending data process. To receive data, the signal extracted by coupling circuit from the power line, filter interference and noise by band-pass filter, after being amplified by the pre-stage amplifier circuit sending into

PL3105 for demodulation, dispreading and decoding. Its communications block diagram is shown in figure 3.

C. Smart Home Control Platform Smart Home Platform is the core of the system, which is the equipment communications bridge between end-user terminals and terminal equipment. The hardware block diagram is shown in figure 4. Just as shown in the figure 4, when the user sends the control instructions by the cell phone terminal, the platform will

Fig. 2. This is the wireless communication module diagram. In this part, CC2430 serves as ZigBee coordinator.

Fig. 3. This is the schematic of PLC communication.

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receive the instruction from the GSM module and analyzed by the MCU. Processed information through PLC communication module is coupled to the power line. When

the room is in dangerous situation, the corresponding information goes through wireless sensor networks, PLC communication module sends to the smart home control platform. After analyzing, the control platform will send a text messages about the corresponding danger to notify the user through GSM module.

IV. SYSTEM SOFTWARE DESIGN The system’s information flow includes from terminal equipment to the user’s control terminal and from user’s terminal to terminal equipment. The way that information reaches their destinations safely and reliably is the key of the system’s design. The idea of this paper is to achieve the address immobilizing. From the system architecture mentioned above, we can see clearly that information from the terminal device to the user’s terminal (mobile phone) flows through the line just like the terminal device (CC2430), coordinator node, smart home control platform, and the user’s mobile phone. User’s mobile phone number fixed namely the mailing address fixed. Considering that each family has only one control platform, so its mailing address can be fixed. Each room just has one coordinator node so its address can also be fixed. Obviously immobilizing device address is an effective solution to this problem. The terminal device address is an 8 bit decimal number which makes up of 5 digits net address and 3 digits network number .while the first three digits network number is corresponding to the room number, the left 5 digits net address corresponding to the 16 bit binary short address. After the terminal equipment interconnects successfully, corresponding LCD screen will show its own 8 digits decimal address, so that users can record the information. When user sends control information to a terminal device, it just sends 8 digits control terminal address and 3 digits control operation code that can achieve right terminal equipment control. The design details will be mentioned in wireless sensor networking, PLC communications and GSM data transmission module part.

A. Wireless Sensor Networks Networking In this paper, we utilize the star topology. Network process mainly consists of two parts: process of the terminal device applicants for address and process of the coordinate allocates addresses to terminal device.

Because each wireless network just has one coordinator node in the system, coordinator establishes a new network directly after its power-on. When switched on, device begins to acquire the network address. Firstly, it begins to search whether there is an existing network around or not. If there is no network around, the device stops accessing address processes and goes back to sleep. If there is a network around, the device proposes adding application, and then judges whether it associates with the network successfully or not. If the association is unsuccessful, the application determines whether the frequency of a row more than three times, if more than three times, the terminal device to stop addressing and flows into the sleep state; if there is no more than three times, it continues to issue the application. When the association is successful, terminal equipments node will get its own 16-bit short address within the nets, and then add address of the coordinator node into its own adjacency table to complete the address application process. When coordinator node receives a new application of joining the network, firstly checks itself whether still has address assignment capability (a coordinator can assign 65536 addresses). If it still has ability to assign an address for a new node, then assigns a unique 16-bit short address to the new node and add the corresponding information to its adjacency table. Finally, returns a successful information, end the process of address assignment. If at that time, coordinator has no address allocation capability, they would send the application node failure association information to end the address assignment process.

B. PLC Communication Protocol If system is able to carry out PLC communication effectively, it must follow certain protocols. The following will makes a brief introduction about frame structure of the data, the carrier transmission process and the carrier reception process. Communication nodes each time send one frame, which include synchronization header, frame header, source address, destination address, data length, data block, checksum seven parts, and a total of 11 bytes. The frame structure shows in Table 1. Header is used to make the system to send and receive synchronization. Due to the fact that power line noise always exists, according to the relevance, continuously sends synchronization header 09H, AFH, can greatly reduce the noise interference [13]. So the frame header account for two consecutive bytes. In order to reduce

TABLE I PLC DATA FRAME STRUCTURE

Name Quantity Unit

Syn. header Frame header

4 2

Bytes Bytes

Source address Purpose address Data length

1 1 1

Bytes Bytes Bytes

Block 1 Bytes Checksum 1 Bytes

Syn. is the abbreviation of synchronization. The synchronization header is made up of 32 bits “1”, which used to achieve frame synchronization. The frame header is consisted of two consecutive bytes 09H, AFH, which is used to reduce the noise interference in the power line.

Fig. 4. This is the diagram of intelligent home control platform, which is the core of the whole system.The PLC Communication Module is just as earlier referred in fig. 3.The GSM Module we used is TC35.

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the clutter interference within the power line system, this paper adopts PL3105 zero-crossing point for data transmission modes. Because of zero-crossing time is short, to ensure reliable data transmission, the data block length of each frame is only one byte. Checksum is used to reduce the error rate, and improve the reliability of system communication. Carrier module uses bus mode to communication, so the carrier module must be normally set to receiving state and different carrier modules must be allocated a different mailing address. Module receives the order to verify the correct and only the same address module is allowed to respond. As the carrier communication speed is relatively much lower, in order to improve the CPU’s efficiency, receiving and sending process are designed for external interrupt mode. Each interruption arriving, carrier mode completes l frame data receiving or sending. The module configuration process as shown in figure 5, select the rate of 500bps, the inside is automatically selects for the l5-bit PN code. After that, carrier communication controller goes into the receiving state, for carrier signal capture and synchronization. Receiving, the capture and synchronization process completed automatically by the carrier communication control unit hardware circuit,

no software components involved. In figure 5, setting the configuration EX2 = 1 that enable INT2, IT2 = 0 signify using falling edge trigger mode. Assigning carrier enable control bit PLM_SSC (EXT_CFG.0) = 1, means INT2 as a carrier communication synchronization signal interrupt. Carrier transceiver control bits PLM_RS (EXT_CTRL.0) = 1, indicates the carrier controller at sending state; while PLM_RS (EXT_CTRL.0) = 0, means the carrier controller in receiving state. Setting up carrier sending reset register, is used to avoid carrier communication module in sending state for a long time, which will lead to the whole communication system out of control. The carrier sending reset register is a 13-bit counter. In sending state, the counter decreasing, when decreasing to 0, the carrier is forced from sending state to receiving state. In receiving state, the counter stops working. If send dates for a long time, register PLM_RST must be written A2H. After writing, the counter automatically resets, carrier

communication module keeps sending state. In receiving process, the carrier communication controls unit dispreading l-bit data to generate an interrupt. First we use an l6-bit receive window to receive communications synchronization header in l-bit sliding way. After receiving frame header successfully, we can intercept follow-up data by using 8-bit one byte manner. In this way, we can get the valid transmitted dates. Among the Receiving process, only the carrier module which receives consistent communication protocol format data, and its address same as the aim address, gives response to the control platform, then receives the communication data. After receiving the data, the carrier module goes into sending state. In sending process, firstly, set the carrier module to sending state, when the carrier communication control unit sends l bits of spread-spectrum data, automatically generates an interrupt to allow the next data transmission. First of all, according to capture and synchronization process requires, carrier module sends at least 32-bit of the all “1”, then send the sync header bits 09H, AFH, finally, according to the communications protocol to send mailing address, data length, data volume, verification, etc. After all the data sent completely, the carrier module is transferred to receiving state. However, in order to ensure the last data to be sent successfully, you must not transferred carrier module to receiving state until the next interrupt arriving. Before carrier module completely sends all the dates, CPU should timely write A2H to register PLM_RST, so that the counter can reset in time to avoid the carrier automatic entering the receive state.

C. Software Design of GSM Data Transfer Module Through the software, GSM (TC35) module can complete the network login, read SIM information, read or send short message and other functions with written AT commands. TC35 can support three message modes: Block Mode, PDU Model and the Text Model. Short Message Service commonly uses PDU Model and Text Model, but the Text Model does not support Chinese SMS. So through the program design, TC35 is set to PDU short message mode.TC35 module will store the receiving message in cache unit or SIM card, according to different parameter setting. From the view of data privacy, this paper adopts the method that store the receiving message in cache unit. In order to ensure redundancy of the memory cell, TC35 perform a delete operation automatically, when the buffer storage capacity reaches to half. Control platform to receive messages from the GSM module, through the AT command “AT + CMGR” read information from the cache. In order to reduce the power consumption of the system, the interrupt mode was used in data sending and receiving process.

V. EXPERIMENTAL RESULTS AND ANALYSIS After all parts of the communication module separate debugged successfully, we use ZigBee module, GSM module and laboratory power line environment practiced together to build communication experimental platform. Specific experimental environment is such, the wireless distance between ZigBee terminal node and coordinator is thirty meters, and we conducted experiments respectively at space

Fig. 5. This is the module configuration flows.

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from ten to fifty meters between the two power lines carrier modules. Laboratory power line environment just like this, ten fluorescent lights whose power is thirty watts, sixteen PC, one printer and one switch. The experimental results show that the experiment environment can achieve data communicating reliably, and the accuracy of data receiving is 100%.In order to simulate the real power channels, we added some man-made interference such as turn on and turn off the fluorescent lamps, opening and closing PC, turning the printer on and off, inserting and pulling plug, etc. In that case, the experiment result is not as good as before. The accuracy of data receiving reduced to 98%. Aim at reducing the interference on the power line, we put forward two measures. First, on the basis of spread spectrum technology, we introduce complement redundancy check (for command word) and cyclic redundancy check (CRC, for general data) to improve the reliability of the data transmission. Second, we using the methods of no response automatic retransmission to reduce the rate of data losing caused by system’s transient disturbance.

VI. CONCLUSION The design we proposed which using the ZigBee wireless sensor networks and PLC combination of information transmission, not only overcomes the traditional cabling complexity but also realizes flexibility about the terminal device enter the smart home network. In function, system using mobile phones remote control to achieve the flexibility and convenience about home-based intelligent device control. In addition, the system uses dual power supply design ideas, and further improves the system’s stability and reliability. Future work will concentrate on high speed data transmission, and especially realize sending home interior picture information to the user in a high speed. In this case, indoor scene image information interaction can be used to improve the performance of the whole system.

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