Applied Mechanics and Materials Vols. 336-338 (2013) pp 1645-1649© (2013) Trans Tech Publications, Switzerlanddoi:10.4028/www.scientific.net/AMM.336-338.1645Design and Realization of Wireless LAN in Smart Home System Based on 433MHZ Communication Zhimin Li 1, a, Dehan Luo1,b, DanJun Fan1,cand Chao Wang1,d 1 School of Information Engineering, Guangdong University of Technology, guangzhou, china ali_zhimin163@163.com Keywords: 433MHZ; smart home; wireless LAN; low consumption; Si4421. Abstract. Nowadays, wireless network technology in smart home is rapid gaining popularity duo to its flexible integration into everyday life. The paper introduces a method that adopts 433MHZ communication to establish the wireless network in smart home system based on Si4421 wireless modules. The paper designed the overall idea of how to establish the wireless network, it mainly talk about the wireless module, including both software and hardware. The difficulty lies in the realization of the custom wireless communication protocol. The Si4421 wireless module was tested in data communication and control in smart home system which can work efficiently and reliably, it proved that the wireless module is perfectly suitable for the wireless network construction in smart home with small size package, low consumption, low cost, and strong ability to leap obstacles. 1. Introduction As the rapidly development of science and technology, smart home are changing life style of 21st century’s human beings. With the advancement in technology, the concept of wireless smart home is being investigated in recent years, which the wireless network technology is widely used. Compared to traditional wire network that the wireless network have a lager number of advantages, it can provide both significant cost savings in a smart home environment, as well as a great level of flexibility and control for the building administrators, and great convenient and comfort for occupants [1], and it is suitable for converting the old ordinary home into modern smart home by avoiding the expensive and disruption of wiring. Moreover, it is easy for update and maintenance. Wireless network technology used in smart home has become a mainstream. There are many commonly used wireless communication technology, such as infrared data transmission (IrDA), Bluetooth, Wifi, gprs, and ZigBee[2], They all have their own characteristics, each suitable for different data communication occasion. the key parameters comparison between each form of commonly used wireless communication is as shown in table 1[2], and the wireless LAN in smart home has the following characteristics[3]： • A small mount of transfer data needn’t high speed. • It should be inexpensive and easy for popularize. • Strong ability to across obstacles in home. • Due to have a variety of appliances in smart home, it should have the capacity of large network. According to the comparison between different wireless communication technology, the 433Mhz communication is fully meet the requirement of wireless network in smart home. This paper is concerned with constructing a wireless network in smart home based on 433MHZ communication, which the wireless module is based on the Si4421. The device has a simple structure, small size, low power consumption, low cost and across obstacles[4], it is ideal for home networking. The network system architecture, wireless module hardware design and software design are introduced as follows. All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP,www.ttp.net. (ID: 183.27.101.10-23/05/13,13:13:30) 1646Industrial Instrumentation and Control Systems IITable 1. The key parameters comparison between different short-range wireless communications Wireless technology ZigBee Bluetooth gprs WiFi IrDA 433 Transmission Frequency 2.4Ghz(global) 868Mhz(Europe) 915Mhz(USA) 2.4Ghz GSM 2.4Ghz 38Khz 433Mhz Transmission speed 250Kbps 20Kbps 40Kbps 1Mbps 171.2Kbps 11Mbps 1.52Mbps 256Kbps Barrier across ability low low medium medium low high Power consumption medium low medium high low low Construction costs Medium high high high low low 2. System Architecture Smart home is highly-efficient, comfortable，safe and convenient living environment which uses a home as a platform and puts the buildings, automation and intelligence in one [1]. Fig.1 shows the system architecture of the wireless LAN in smart home, it mainly consists of three parts: smart gateway, 433MHZ wireless communicate module and smart appliance. Due to the household appliances uncertainty replacement properties, the wireless networks often need to add or reduce some smart household appliances, the wireless LAN adopts star network structure, the smart gateway can communicate with smart appliances through wireless network, which the wireless network is depended on 433Mhz wireless communication module, the smart gateway equipped with master wireless module and the smart appliances equipped with slave wireless module, in this way, the smart appliances can centrally manage and control by smart gateway through the wireless LAN[1]. Applied Mechanics and Materials Vols. 336-3381647are integrated, Only an external crystal and bypass filtering are needed for operation. The schematic diagram of the wireless module is shown in Fig.4. The advantages of the designed wireless module are as follows: • Low power consumption, 2.2 to 3.8V supply voltage, Low standby current (0.3 µA). • Adopt SPI communication, High bit rate up to 115.2 kbps • Strong penetration ability, Indoor transmission distance up to 50 m. • Simple construction and low cost, the frequency band of 433MHZ is license free frequency bands [2]. • Strong anti-jamming capability and low error rate Fig 3. The structure of wireless module Fig .4 Wireless communication module schematic diagram 4. Software Design The software design is the importance and difficulty of the system, it related to the performance of the wireless network[6], the custom wireless communication protocol and the framework of the program are introduced as follows. 4.1 The custom wireless communication protocol In radio frequency communications, it often exist a lot of interference signals, the wireless communicate module may randomly send some invalid data that the processor even without sending data or instructions[7], in order to ensure the reliability of the appliances data transmission in the entire wireless network in smart home, it is necessary to design a wireless communication protocol to avoid data collisions and standardize the transmission of wireless data . the wireless communication protocol can improve the anti-jamming performance of the system. the structure of custom appliances wireless communication protocol was shown in Fig. 5 , it includes the direct section ,length section, control section, data section, CRC section and the affirm section . Direct section 2 byte Frame length 1 byte Length section 1 byte Frame control 2 byte Control section 1 byte Frame sequence 2 byte Data section 0~200 byte Source address 4 byte CRC section 1 byte Objective address 4 byte Affirm section 1 byte Appliances data … Fig .5 The packet structure of appliances transmission protocol The custom wireless communication protocol mainly used to regulate the communication between the master device and sub device, which the master device contain the master wireless module and the sub device contain the slave wireless module. The data and control instructions of appliances transmit in the custom packet form via the wireless module [6].The first byte of the data interaction was sent by the master wireless module, it determine the direction of data transmission, in which data 0x0f0f means the data transmit from master device to sub device, and data 0xf0f0 means the data transmit from slave device to master device. If the data transmission is from master device to slave device (direct section is 0xf0f0), then the length section, control section, data section and the CRC section were sent by the master device, the affirm section was sent by the sub device. Similarly if the data 1648Industrial Instrumentation and Control Systems IItransmission is from sub device to master device (direct section is 0x0f0f), then the length section, control section, data section and the CRC section were sent by the sub device, the affirm section was sent by the master device. The control section mainly used to manage the data transmission of the wireless network, it has several types, includes data frame, affirm frame, module busy frame, sub address frame, main address frame, network frame and so on. The structure of data section was shown in Fig.6. It contain the detail information of the smart appliances, such as the product type, manufacture company, product ID and the various status of the product functions. The CRC section was used for verification and the affirm section was used to judge whether the data is correct, which the code 0X12 means the receive data was the same to the send data and the code 0X21 means the data has transmission error. All in all, the protocol provides a more flexible and more convenient control for the wireless data transmission in smart home system[7]. Product type 2 byte common Function codes 1 byte 0x01 (open) 0x02( close) Manufacture company 2 byte Parameter values 1 byte 0 0 Product model 4 byte Private functions 1 byte Place of production 2 byte Private functions codes ID number 4 byte Private parameter values Common functions 1byte 0x02 … Fig .6 The data structure of the appliances 4.2 The framework of program The program flowchart of master device is shown in Fig .7. The master wireless module send the main address to slave wireless module, when the slave wireless module receive the main address it would feedback an affirm frame, if the master module did not receive the affirm frame it would send the master address again. The wireless network would be established after it receive the affirm frame, then the status of the master wireless module was checked, if it is the network frame, it means the slave device was already join the wireless network, then the master should record the smart appliances’ ID (Each smart appliance has a unique ID code) and update its status, and if it is the data frame, it means the smart appliances send its status to gateway. if it is the address frame , it means had smart appliances apply to join the wireless network, the gateway should assign new address for the appliances. The status of the gateway was checked after the enquiry of the master wireless module, it would send the instructions to smart appliances if it had constructions, and it would return to check the wireless module. Similarly, it program flowchart of the slave device is shown in Fig .8. Fig .7 The program flowchart of master device Fig . 8 The program flowchart of slave device Applied Mechanics and Materials Vols. 336-33816495. Conclusions Wireless communication technology has been gradually used in smart home system, wireless control system in smart home can provide both significant cost saving in a home environment, as well as a great level of flexibility and control for the building administrators, and great comfort for the occupants[1]. This paper proposed a new effective method based on 433MHZ to build a wireless LAN in smart home. The way to build wireless LAN in smart home proposed in this paper features a high reliability, small size, low consumption, low cost and easy to realize [7]. It provides the possibility for the popularity of smart home and it has an excellent applicability and popularization value. References [1] Dae-Man Han and Jae-Hyun Lim,” Smart Home Energy Management System using IEEE 802.15.4 and ZigBee”, Consumer Electronics, IEEE Transactions on, vol. 56,2010,pp. 1417 - 1425. [2] Dai QingYun, BaoHong Liu, Yihong Liu, Zexi, Zhou Ke, Wang Jin, “433MHz Wireless Network Technology for Wireless Manufacturing”. Second International Conference on Future Generation Communication and Networking ,2008, pp.393-397 [3] Qi Zhen-xing, Discuses the development of China's Smart Home, Guangxi Journal of Light Industry, 2009, pp 63 - 64 . [4] Das.Subir Kumar, Ohba. 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