A zig bee based home automation system


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A zig bee based home automation system

  1. 1. IEEE Transactions on Consumer Electronics, Vol. 55, No. 2, MAY 2009Contributed PaperManuscript received November 8, 2008 0098 3063/09/$20.00 © 2009 IEEE422A ZigBee-Based Home Automation SystemKhusvinder Gill, Shuang-Hua Yang, Fang Yao, and Xin LuAbstract — In recent years, the home environment has seen arapid introduction of network enabled digital technology. Thistechnology offers new and exciting opportunities to increasethe connectivity of devices within the home for the purpose ofhome automation. Moreover, with the rapid expansion of theInternet, there is the added potential for the remote controland monitoring of such network enabled devices. However,the adoption of home automation systems has been slow. Thispaper identifies the reasons for this slow adoption andevaluates the potential of ZigBee for addressing theseproblems through the design and implementation of a flexiblehome automation architecture. A ZigBee based homeautomation system and Wi-Fi network are integrated througha common home gateway. The home gateway providesnetwork interoperability, a simple and flexible user interface,and remote access to the system. A dedicated virtual home isimplemented to cater for the system’s security and safetyneeds. To demonstrate the feasibility and effectiveness of theproposed system, four devices, a light switch, radiator valve,safety sensor and ZigBee remote control have been developedand evaluated with the home automation system.Index Terms — Home Automation, ZigBee, Sensor Network.I. INTRODUCTIONIn recent years the introduction of network enabled devicesinto the home environment has proceeded at an unprecedentedrate. Moreover, with the rapid expansion of the Internet, thereis the potential for the remote control and monitoring of suchnetwork enabled devices. However, the new and excitingopportunities to increase the connectivity of devices within thehome for the purpose of home automation remain largelyunexploited.A.Existing Home Automation TechnologiesThere are many definitions of home automation available inthe literature. [1] describes home automation as theintroduction of technology within the home to enhance thequality of life of its occupants, through the provision ofdifferent services such as telehealth, multimedia entertainmentand energy conservation.There has been significant research into the field of homeautomation. The X10 industry standard, developed in 1975 forcommunication between electronic devices, is the oldeststandard identified from the author’s review, providing limitedcontrol over household devices through the home’s powerlines. Recently, research into the field of home automationK. Gill, S. H. Yang, F. Yao and X. Lu are with the Computer ScienceDepartment, Loughborough University, Loughborough, England, LE11 3TU(e-mail: s.h.yang@lboro.ac.uk).has continued to receive much attention in academia. [2]developed a Java based home automation system. Anembedded board physically connected all the homeautomation devices and, through integration with a personalcomputer (PC) based web server, provided remote access tothe system. The use of Java technology, which incorporatesbuilt-in network security features, produces a securesolution. However, the system requires an intrusive andexpensive wired installation and the use of a high end PC.[3] introduced a Bluetooth based home automation system,consisting of a primary controller and a number of Bluetoothsub-controllers. Each home device is physically connectedto a local Bluetooth sub-controller. The home devicescommunicate with their respective sub-controller usingwired communications. From the sub-controller allcommunications are sent to the primary controller usingwireless communications. It is desirable for each homedevice to have a dedicated Bluetooth module. However, dueto the fiscal expense of Bluetooth technology, a singlemodule is shared amongst several devices. This architecturereduces the amount of physical wiring required and hencethe intrusiveness of the installation, through the use ofwireless technology. However, the architecture does notcompletely alleviate the intrusiveness of the installation dueto the incorporation of some wired communications.Moreover the sharing of a single Bluetooth module betweennumerous devices has the disadvantage of incurring anaccess delay. [4] introduced a phone based remote controllerfor home and office automation. The system differs in thatall communications occur over a fixed telephone line andnot over the Internet. The system can be accessed using anytelephone that supports dual tone multiple frequency(DTMF). The disadvantages of this system are threefold:users are not provided with a graphical user interface, usershave to remember an access code, and they have toremember which buttons to press for the control ofconnected devices. [5] proposed a novel control network,using hand gestures. The controller uses a glove to relayhand gestures to the system. The problem with the systemlies in the inaccuracy of hand gestures, with the potential fornormal arm movements being inaccurately interpreted ascommands. Moreover, there is the risk of user fatigue ifrepetitive hand gestures are required.The introduction provides a short review of the existingacademic research into home automation. The publicallyavailable research into home automation lies predominantly inthe academic arena, with little industrial research beingpublically available. The adoption of home automationtechnologies into commercial systems has been limited, andwhere available consumer uptake has been slow.The aforementioned systems offer little in the way ofinteroperability. Attempts have been made to provide network
  2. 2. K. Gill et al.: A ZigBee-Based Home Automation System 423interoperability and remote access to home automationsystems through the development of home gateways. [6]defined a home gateway as the point of ingress between apersonal area network and a public access network. Theydeveloped a web server based home gateway to interconnectIEEE1394, with a power line based home automation system,and the Internet. To make the system more attractive to homeowners, a real time AV transcoding capability was included.The system offers an insightful look into the development of ahome gateway; however, the use of power lines as thecommunication medium limits the positioning of deviceswithin the home to areas in close proximity to power sockets.[7] proposed a home energy management focused homegateway, which connects the home network with the Internet.The system was installed in twenty houses in the Tokyo area.[8] proposed a home gateway based on the OSGI (OpenService Gateway Initiative), which allows service providers toaccess home automation systems for administration andmaintenance services. The proposed system is divided intotwo subsystems. The first is the DSM (Digital Home ServiceDistribution and Management System), which provides a userinterface for the control and monitoring of connected homeautomation devices. The second is the Home Gateway, whichis responsible for managing the home automation system. Thisopen architecture raises privacy problems which, for someusers, may be much greater than the advantages offered bygranting third party access. [9] implements a home gatewaythat accepts mobile phone signals and activates or deactivatesa LED representing a home device.These systems have made a significant contribution to thedevelopment of a home gateway. However, the existingnetwork infrastructure within the home environment has notbeen taken into consideration when selecting the networks forintegration with the respective home gateways. Moreover, theexisting research has focused on the provision of remoteconnectivity and has largely neglected investigating theintegration of existing local networks.B.Analysis of the Existing SystemsThe adoption of home automation technology by consumershas been limited. We propose that, from the home automationdomain analysis, the problems limiting wide spread consumeradoption can be grouped into five general categories. Firstly,complex and expensive architecture: the existing systemsarchitectures generally incorporate a personal computer forthe purposes of network management and provision of remoteaccess. This adds additional complexity to the system, henceincreasing the overall fiscal expense. Secondly, intrusiveinstallation: the majority of systems require varying levels ofphysical wiring in their architectures. This, in some cases, isdue to the expense of the alternative wireless technologies.Hence, these systems require intrusive and expensiveinstallations. Thirdly, lack of network interoperability: bothhome networks and the home automation systems whichutilise them have been developed and adopted in an unplannedand ad-hoc manner. This has lead to a home environmentconsisting of a complex maze of heterogeneous networks.These networks and the systems that utilise them normallyoffer little interoperability; leading to three potential problems• duplication of monitoring activities, due to lack ofinteroperability;• the possibility of interference, between co-existingnetworks; and• the potential for two simultaneous, autonomousactions on co-existing networks, interacting andresulting in an undesirable outcome.Fourthly, interface inflexibility: the existing systems offervarying approaches for users to control and monitor theconnected devices. However, this is normally limited to asingle method of control, which offers users limitedflexibility. The systems which provide more than one interfacedevice normally provide different user interfaces and riskconfusing users. Finally, security and safety: the existingapproaches have not focused on security and safety problemsthat may arise from their implementation. Moreover, thesystems that offer some degree of security have neglected theproblems with sharing information between devices producedby multiple vendors for the purposes of establishing security.C.Features of the proposed SystemThis paper presents a novel, stand alone, low-cost andflexible ZigBee based home automation system. Thearchitecture is designed to reduce the system’s complexity andlower fiscal costs. Hence, the system endeavours not toincorporate complex and expensive components, such as ahigh end personal computer, where possible. The system isflexible and scalable, allowing additional home appliancesdesigned by multiple vendors, to be securely and safely addedto the home network with the minimum amount of effort. Thesystem allows home owners to monitor and control connecteddevices in the home, through a variety of controls, including aZigBee based remote control, and any Wi-Fi enabled devicewhich supports Java. Additionally, users may remotelymonitor and control their home devices using any Internetenabled device with Java support. A home gateway isimplemented to facilitate interoperability betweenheterogeneous networks and provide a consistent interface,regardless of the accessing device.A virtual home pre-processes all communications beforethey are realised on the real home automation system. Allcommunications are checked for security and safety beforebeing allowed to continue to their respective destinations.This paper is organised as follows: Section 2 discusses thedeveloped home automation architecture, including a reviewof the technology used. Section 3 describes theimplementation of the proposed system. Section 4 provides adiscussion of the system evaluation and Section 5 provides aconclusion.II. SYSTEM ARCHITECTUREThis section describes the conceptual design of a flexibleand low cost home automation infrastructure (see Figure 1).The home’s low data rate, control and monitoring needs arecatered for using Zigbee. The home’s high data rate needs,such as multimedia applications, are met by the Wi-Fi (IEEE802.11g) standard.
  3. 3. IEEE Transactions on Consumer Electronics, Vol. 55, No. 2, MAY 2009424Fig. 1. Conceptual Architecture Overview.A home gateway is implemented to provide interoperabilitybetween the heterogeneous Zigbee and Wi-Fi networks, andfacilitate local and remote control and monitoring over thehome’s devices. A virtual home is implemented for the provisionof real time security and safety for the home and its inhabitants.As depicted in Figure 1, the proposed system consistsprimarily of four steps. Remote user can access the systemusing the Internet. The remote user’s communications traversethe internet until they reach the home network. They are thenwirelessly transmitted to the Home Gateway using the homesWi-Fi network. The Home Gateway is integrated with avirtual home. These communications are checked andprocessed by the home gateway and virtual home, asdiscussed in greater detail later. This checking processinvolves communication with the home networks coordinator,which is integrated with the home’s device database andcontains the status of all connected devices. Once checked thecommunications are sent to the real home automation systemand the respective device. Additionally, a local ZigBee basedremote control can be used to directly control connecteddevices.A.Residential NetworksAs discussed, the proposed system architecture implementsa ZigBee based home automation network and a Wi-Fi basedmultimedia network. Alternative standards could have beenintegrated with the home gateway. However, the use ofZigbee and Wi-Fi offers certain advantages. Zigbeetechnology is designed to be used on applications that requirelow data rate, low-cost, low power consumption, and two waywireless communications. The Wi-Fi standard is designed toprovide relatively high data rate communications. Wi-Fi hasthe advantage of an existing and wide spread presence inhomes in the United Kingdom. The combination of Zigbeeand Wi-Fi technologies has the potential to provide acomprehensive home automation solution.Zigbee technologyZigBee is a radio frequency (RF) communicationsstandard based on IEEE 802.15.4. Figure 2 depicts the generalarchitecture of a Zigbee based home automation network. TheZigbee coordinator is responsible for creating and maintainingthe network. Each electronic device (i.e. Washing Machine,Television, Lamp etc) in the system is a Zigbee devicemanaged by the coordinator. All communication betweendevices propagates through the coordinator to the destinationdevice. The wireless nature of ZigBee helps overcome theintrusive installation problem with the existing homeautomation systems identified earlier. The ZigBee standardtheoretically provides 250kbps data rate, and as 40kbps canmeet the requirements of most control systems, it is sufficientfor controlling most home automation devices. The lowinstallation and running cost offered by ZigBee helps tacklethe expensive and complex architecture problems withexisting home automation systems, as identified earlier.Wi-Fi TechnologyIn the proposed system architecture, Wi-Fi is used for twoprimary purposes. Firstly, it is the chosen communicationstandard for multimedia applications in the home. Secondly, itis used to provide access to the home automation system fromWi-Fi enabled devices, as an alternative to the Zigbee basedlocal controller. This approach was taken because homesincreasingly have Wi-Fi networks and Wi-Fi enabled devicessuch as PDA’s and mobile phones. The additional cost of aZigbee based controller in these situations is unwarranted.Moreover, the high data rate nature of Wi-Fi allows forgreater flexibility in interface design. Wi-Fi implements theIEEE 802.11 standard and offers wireless networking throughthe use of radio frequency. There are different versions of thisprotocol. The dominant protocol in use today is IEEE802.11g, which operates in the unlicensed 2.4 GHz band andprovides a maximum raw data rate of 54 Mbps.
  4. 4. K. Gill et al.: A ZigBee-Based Home Automation System 425Fig. 2. Zigbee Home Automation Architecture.The use of Wi-Fi offers several advantages over alternativetechnologies. The Wi-Fi standard is more established inhomes in the UK than alternatives such as Bluetooth as awireless home networking technology. The result is lessequipment expense for the consumer, and the use of atechnology users are familiar with.Network CoexistenceHeterogeneous and homogenous home networks may co-exist with each other in the same environment. The problem ofinterference between these networks increases as more andmore standards emerge which use the same communicationmediums. The interference problems between the possiblestandards have been investigated. [10] researched the co-existence of Zigbee, Bluetooth and Wi-Fi. The three protocolsuse the same 2.4 GHz ISM band. It was found that Zigbeeinterference has an insignificant effect on Wi-Fi throughput.The effect of Wi-Fi on Zigbee throughput is a 10% reductionin throughput, which provides an operational solution. Theexperiment was repeated using Wi-Fi and Bluetooth. Theresults showed a significant reduction in Wi-Fi throughputand Bluetooth throughput. It can be concluded that the use ofthe unlicensed part of the wireless spectrum by Zigbee causesinterference problems. Technologies such as Bluetooth,microwave ovens and cordless telephones can causeinterference with Zigbee [11]. However, Zigbee and Wi-Fican exist together with less interference problems thanalternative technologies currently available, hence offering thebest combination available for use in our purposedarchitecture.B.Home GatewayThe home gateway, as depicted in Figure 1, is charged withproviding interoperability between different connectingnetworks. The home gateway provides two primary functionsfor the proposed architecture. Firstly, the home gatewayprovides data translation services between the Internet, Wi-Fi,and ZigBee networks. Secondly, the home gateway provides astandardised user interface for devices connecting to theZigBee home network, remotely using the Internet or locallyusing the Wi-Fi network. The home gateway does not providea standardised interface for the local ZigBee remote control(See Figure 1). This decision was made to provide greaterfreedom for interface design and avoid limitations that have tobe taken into consideration in the design of the low data rate,low power ZigBee remote control interface. Although, asdepicted, the close cooperation between the home gatewayand device database allows for the real time control andmonitoring of all home devices, regardless of the accessdevice and network used. The home gateway is implementedin the system architecture to overcome the problem ofinsufficient network interoperability, identified in existinghome automation approaches. Moreover, the proposedapproach looks at the existing network structure within thehome environment and integrates networks which arepredominantly established in the existing home environment.Additionally, the home gateway reduces the inflexibility in thecontrol modes of existing home automation systems; this isundertaken through the prevision of manual, local and remotecontrol. Furthermore, the interface of the controlling devicesis standardised across the control modes.C.Virtual HomeThe virtual home, as depicted in Figure 1, is responsible forthe administration of security and safety for the homeautomation system. The virtual home, as the name suggests, isa virtual environment where the actions requested by users arechecked. For the purposes of security, all the messagesreceived by the virtual home are checked by authenticating thesenders, checking the integrity of the messages to ensure theyhave not been tampered with, and protecting theconfidentiality of messages through the use of encryption. Thesystem’s safety is protected by ensuring the commandsreceived are appropriate for the respective home network andthat all changes requested fall within the specified safetylimits. The primary objective of the virtual home is to preventany event that may pose a security or safety concern fromimplementation in the home networks. The virtual home isincluded in the proposed architecture to tackle the security andsafety problems.D.Device EngineThe home automation system is designed to be flexible,allowing different devices designed by multiple vendors to beconnected. Each device incorporates a dedicated engine,responsible for providing the necessary applicationfunctionality and ZigBee network connectivity. Moreover,each device engine may contain dedicated security and safetymeasures. Critical devices should check all requestedoperations to ensure that they will not result in an undesirableoutcome. Furthermore, collaboration with the virtual homeshould provide the necessary information to facilitate securecommunications.III. SYSTEM IMPLEMENTATIONThe implementation of the proposed system is illustrated inFigure 3. As depicted, a ZigBee based home automationsystem is implemented for the monitoring and control ofhousehold devices. To cater for the household’s high data rateneeds, such as multimedia entertainment, a Wi-Fi network isimplemented. A home gateway has been developed to provideinteroperability between these networks. The home gatewaypresents a unified interface for users to locally and remotelyaccess home networks. The security and safety of the homeautomation network is realised through the development of theearlier described virtual home on the Home Gateway. Todemonstrate the feasibility and effectiveness of the proposed
  5. 5. IEEE Transactions on Consumer Electronics, Vol. 55, No. 2, MAY 2009426Fig. 3. System Implementation.system four devices, a light switch, radiator valve, safetysensor and ZigBee remote controller have been developed andintegrated with the home automation system. This sectionprovides a thorough discussion of the system implementation.A.ZigBee Home Automation NetworkThe ZigBee home automation network consists of acoordinator, routers and several end devices. The coordinator isresponsible for starting the ZigBee network. During the networkinitialisation phase, the coordinator scans the available radiochannels to find the most suitable. Normally this will be thechannel with the least activity, in order to reduce the level ofinterference. It is possible to limit the channels scanned, forexample excluding those frequencies ranges used by the Wi-Finetwork included in the proposed architecture. However, ourexperiments have shown that the average time taken to scan allthe available channels is 9 seconds (to the nearest second). Thisscan time is relatively small and as the home coordinator isinitialised infrequently this is an acceptable delay whencontrasted with the performance increase possible through theuse of a channel with less interference. The coordinator is pre-programmed with the PAN ID (Personal Area NetworkIdentifier), although it is possible for the coordinator todynamically scan for existing network PAN IDs in the samefrequency and generate a PAN ID that does not conflict. Allhome devices connected to the ZigBee home automationnetwork are assigned a fixed 64 bit MAC address. Additionally,each device is assigned a dynamic 16 bit short address that isfixed for the lifetime of the network. At this stage of thenetwork initialisation, the coordinator assigns itself the shortaddress 0x0000. After the coordinator’s initialisation phase thecoordinator enters “coordinator mode”, during this phase itawaits requests from ZigBee devices to join the network.The ZigBee devices developed for the home network, asmentioned, includes a light switch, radiator valve, safety sensorand ZigBee remote control. A ZigBee end node has beenintegrated with these devices. As the devices are started, duringtheir respective initialisation stage, the node scans for availablechannels to identify the network it wishes to join. There may bemultiple networks in the same channel, these networks arenormally distinguished by their PAN ID. The node selectswhich network to join based on the PAN ID. The node sends arequest to the network coordinator to join the network. Therequest is sent to the coordinator directly or through aneighbouring router on the desired network with which the nodeshares the best signal. On receipt of the request the coordinatorjudges whether the requesting device is permitted to connect tothe home automation network. The standard implementation ofmost ZigBee networks prevents unauthorised devices joiningthe network by providing a short user defined period wheredevice may join. This, in our opinion, does not on its ownprovide sufficient network security. To enhance the systemssecurity the proposed system encrypts all devicecommunications including the requests to join the homenetwork with a private key. Only those devices that are inpossession of the correct private key can successfully connect tothe home network. The devices that are permitted to join thenetwork are recorded in the device database and stored on thenetwork coordinator. A partially connected mesh topology wasadopted for the ZigBee home automation network. Due to thenature of the home environment where communicationinterference is constantly fluctuating, the advantage of increasedcommunication routes available through the adoption of a meshtopology outweighs the added routing complexity.B.Wi-Fi NetworkThe homes Wi-Fi network was implemented through astandard Wireless (802.11b and 802.11g) ADSL ModemRouter, with a 4 port switch. The modem provides twoprimary functions. Firstly, the modem provides theconnection between the Internet and local Wi-Fi network;hence extending access to the Wi-Fi enabled home gatewayto any location with Internet access. Secondly, any local Wi-Fi enabled device within range of the home’s Wi-Fi networkcan directly access the home gateway. This provides a lowcost communication method with the home network,reduced infrastructure costs where Wi-Fi devices are alreadyin use. Moreover, home owners can monitor and control thehome automation network, using familiar technology anddevices.C.Home GatewayA thorough review of existing home gateway technologiesrevealed that no off-the-shelf solution exists that provides thefunctionality specified in the requirements for the homegateway, as previously discussed. This included the provisionof interoperability between the Internet, Wi-Fi and ZigBeenetworks. Hence, it was necessary to develop a bespoke homegateway, as shown in Figure 4. The home gateway consists ofa Wi-Fi module, a ZigBee Microcontroller and a powersupply. The Wi-Fi module provides low cost and embeddedserial to Wi-Fi connectivity. The ZigBee Microcontrollerprovides the connection to the ZigBee network. The Wi-Fimodule connects to the home’s local Wi-Fi network and theZigBee microcontroller connects to the ZigBee home networkas an end device. The home gateway once started enters theconfiguration stage. During the configuration stage theembedded Wi-Fi module establishes a connection with a localWi-Fi network.
  6. 6. K. Gill et al.: A ZigBee-Based Home Automation System 427Fig. 4. Home Gateway.The parameters for the Wi-Fi connection such as networkSSID and security parameters are preconfigured.Simultaneously, the ZigBee microcontroller searches for aZigBee home network and, as discussed, establishes aconnection. As with the Wi-Fi module, the ZigBeemicrocontroller’s connection parameters are preconfigured.This concludes the configuration stage.Once the home gateway has been initialised, an idle stateis entered into until input is received. Input can originatefrom both the Wi-Fi network for input to the ZigBeenetwork, or conversely from the ZigBee network for outputto the Wi-Fi network. Input from the Wi-Fi networknormally takes the form of commands from user interfacedevices. The input from the ZigBee network normally takesthe form of responses to commands received earlier fromuser interface devices.D. Virtual HomeThe virtual home is a software construct developed in C.The virtual home is implemented on the home gateway. Allcommunication and instructions are checked, as illustratedin Figure 5, for security and safety, in the virtualenvironment, before implementation in the real homeenvironment. The virtual home waits for input from anexternal source. All devices on the ZigBee networkincorporate the ZigBee microcontroller and a dedicatedAES Coprocessor. Sensitive communications on the homenetwork are encrypted. Hence, the message payload ofsensitive communications received by the virtual homefrom legitimate sources will be encrypted with a validsymmetric key. Once the security of messages has beenestablished, the virtual home checks the safety implicationsof the messages. After decryption the destination deviceaddress is extracted from the message and checked in thedevice database for its existence. Once the device’sexistence on the network has been established, thecommand and parameters included in the message areextracted. The existence of the command for the respectivedevice is checked to ensure the real device offers therequested functionality. The extracted parameters arecompared against predefined safe ranges for the respectivedevice and command. Only after the message has beenprocessed by the virtual home algorithm for security andsafety and declared safe is the message is re-encrypted andforwarded to the real home network device.E.User Interface DevicesTo evaluate the effectiveness of the system architecture forthe provision of easy to implement, and flexible modes ofcontrol; three control modes were developed.Fig. 5. Virtual Home Flow Chart.ZigBee Remote Control: A low cost, simple-to-use remotecontroller, for the local monitoring and control of devices wasdeveloped. The controller board includes a ZigBeemicrocontroller, LCD display, four push button switches, andis powered by four AA batteries. Instructions from the remotecontrol traverse the home network until received by thedestination device.Remote Access Device and Wi-Fi Remote Control: A standardmobile phone with built in support for Wi-Fi and J2ME wasused to access and control the system. While locally accessingthe system the mobile used Wi-Fi to freely access and controlthe system. When a Wi-Fi connection was not available themobile established an Internet connection to access andcontrol the system. In both scenarios the instructions sent fromthe mobile phone are received by the home gateway, which
  7. 7. IEEE Transactions on Consumer Electronics, Vol. 55, No. 2, MAY 2009428translates the communication and forwards it to the virtualhome, as discussed, before being sent to the destinationdevice.F.Home Automation DevicesTo demonstrate the feasibility and effectiveness of theproposed system three devices; a light switch, radiator valve,and safety sensor, were developed. These devices are depictedin figures 6 (a), (b), and (c) respectively.a. b. c.Fig. 6. (a) ZigBee operated light bulb in the off state; (b) ZigBee basedautomatic radiator valve; (c) ZigBee safety sensor.Light Switch: A conventional light switch was integrated witha ZigBee microcontroller, as shown in Figure 6 (a). In thisprototype the user could access the light switch, detect thelights current state (“On” or “Off”), and adjust the stateaccordingly.Radiator Valve: A prototype automatic radiator valve wasdeveloped and integrated with a ZigBee microcontroller, asshown in Figure 6 (b). The valve can be manually controlledas are conventional valves, but also remotely monitored andcontrolled.Safety Sensor: The safety sensor has special characteristics ofinterest. For instance, unlike most devices, the safety sensorhas to continuously monitor its environment and providefeedback. This reduces the time the device can operate insleep mode, hence considerably reducing the battery life. Asafety sensor was developed (see Figure 6 (c)) to investigatethe potential viability of the system with a mass market enddevice that places a large demand on system resources. Thesafety sensor developed incorporated temperature, carbonmonoxide, flame, and smoke sensors.G.System ConfigurationThis section has described in detail the individual elementsthat combine to implement the proposed system architecture.A user can login to monitor and control the home automationsystems end devices, using one of three user interface devices(ZigBee remote control, Wi-Fi remote control, and Remoteaccess device). All messages from the devices using theInternet for communication are sent to the home’s IP address.The messages are forwarded to the home gateway’s IP addresson the local Wi-Fi network, through a Wi-Fi enabled ADSLmodem. Similarly, communications from the devices using theWi-Fi network for communications are forwarded to the homegateway’s IP address. Once the home gateway has receivedthe messages they are forwarded to the virtual home.Messages from the ZigBee controller are sent directly to theend devices, over the ZigBee network. The virtual homechecks the security and safety of all received messages. Thosemessages that fail to validate are rejected, the validatedmessages are forwarded to the destination device on the realhome network. All responses from the device (i.e.acknowledgments, device status notifications, sensorreadings) are relayed from the device, through the ZigBeenetwork to the virtual home, through the home gateway,across the Wi-Fi network and, where appropriate, across theInternet to the user interface device.IV. EVALUATIONThe implemented system was evaluated both quantitativelyand qualitatively. To demonstrate the feasibility andeffectiveness of the proposed system, four devices, a lightswitch, radiator valve, safety sensor and ZigBee remotecontrol have been developed and integrated with the homeautomation system. These systems were subjected to a cycleof strenuous operations to simulate a high level of everydayusage. The light state was changed 20 times using the ZigBeeremote control and 20 times using the Wi-Fi controller.Similarly the radiator valve state was changed 20 times usingthe ZigBee controller and 20 times using the Wi-Fi controller.The experiments showed the correct functionality of thedevices 100% of the time. Table 1 provides a summary of theaverage delay between request and implementation of therequested change using the Zigbee and Wi-Fi controllers.TABLE 1ZIGBEE AND WI-FI CONTROLLER ACCESS DELAYLight Switch Radiator ValveZigBee Controller accessdelay in ms670 *N/AWi-Fi Controller accessdelay in ms1337 613*N/A indicates that the time delay was too short to be recorded by the testequipment.As Table 1 indicates, the average access delay was greater forthe Wi-Fi controller than for the ZigBee controller. However,the ZigBee controller had an average access delay of 670 mswhile controlling the light switch, whereas the access delayincurred for controlling the radiator valve was small andsubsequently could not be measured with our recordinginstruments. This implies that the majority of the access delaylies in the actuation of the light switch and subsequent bulbstate change and is not attributable to the method of control.This is shown with a N/A in Table 1. Taking this into accountthe access delay for the light bulb (1337 ms) can be adjustedby removing the 670 ms access delay attributed to the switchactuation to provide a more realistic access time for the Wi-Ficontroller for the light switch of 667 ms. This average accessdelay is supported by the access delay recorded for theradiator valve of 613 ms.The viability of the home automation architecture wasevaluated through real world testing of the proposed systemwith the developed radiator valve. The radiator valve, asdepicted in Figure 6 (b), was tested in a real house. Theradiator valve was located in the test house’s living room, on
  8. 8. K. Gill et al.: A ZigBee-Based Home Automation System 429the ground floor as depicted in Figure 7. The radiators existingTRV valve was replaced with the prototype automatic radiatorvalve. The local controller was put on a desk 2m away fromthe radiator and connected to a laptop. This configurationallowed test software running on the local controller to printout the desired temperature set by the user, currenttemperature around the radiator and time taken to reach thedesired temperature by the automatic radiator valve. Figure 8shows the experimental environment.Fig. 7. Radiator Valve ReplacementThe results of the experiments are summarised in Figure 9.The graph shows the desired temperature set by the user (SetPoint) against the actual temperature (Measured Value) of theradiator at a regular interval of 15 minutes. As depicted, theactual temperature of the radiator quickly adjusted to thedesired temperature set by the user, and this holds true formost temperature ranges set by the user. However, the actualtemperature could not reach 25 Co, it was surmised that theradiator was too small to heat such a large room to thistemperature. The evaluation of the radiator valve shows theapplicability of the proposed system with a real world endproduct. The experimentation highlighted that a radiator valvecould successfully be implemented using the ZigBeecommunication standard and monitored and controlled usingthe proposed system. This successful evaluation supports anddemonstrates the potential of the proposed system to be easilyadaptable from the lab environment to the commercial market.Fig. 8. Experimental EnvironmentFor the qualitative analysis of the proposed system, a focusgroup was conducted on the 4thof March 2008 to evaluate enduser’s perspectives of the proposed architecture and obtainfeedback as to areas for further work. The focus groupconsisted of ten members from a UK Housing Association(HA) who were chosen to reflect the views of the endcustomers. From the comments made the majority ofparticipants felt that the proposed system’s ability to remotelydiagnose and check potential errors with systems such asFig. 9. Set Temperature and Measured Temperaturecommunal lighting was an attractive feature. Currently the HAspends approximately £100k on monitoring and maintainingcommunal lighting. The ability to detect when lighting hasmalfunctioned without physical human monitoring wouldmake significant savings and incentivise the investment andadoption of such a system. Additionally, the flexible andextensive range of interfaces offered for the control andmonitoring of devices connected to the home automationnetwork was felt to be an attractive feature. It was felt that thisfeature would benefit people with mobility problems the most.One area for improvement that was highlighted by aparticipant and received widespread acceptance by the groupwas the suggestion to allow users to directly access the homeautomation system from a mobile phone without the need fora physical Internet connection to the home.V.CONCLUSIONThis paper has reviewed the existing state of homeautomation systems, and identified and discussed five areasthat have hindered consumer adoption of such technologies.Briefly, the areas include: the complexity and expense of thearchitectures adopted by existing systems, the intrusiveness ofthe system installations, the lack of interoperability betweendifferent home automation technologies, and the lack ofinteroperability between systems developed by differentmanufacturers that utilise the same technology. Interfaceinflexibility and the inconsistent approaches adopted towardssecurity and safety are also problems. A novel architecture fora home automation system is proposed and implemented,using the relatively new communication technology ZigBee.The use of ZigBee communications technology helps lowerthe expense of the system and the intrusiveness of therespective system installation. The incorporation of the virtualhome concept coordinates the systems security and safetyefforts in a clear and consistent manor. The inclusion of a
  9. 9. IEEE Transactions on Consumer Electronics, Vol. 55, No. 2, MAY 2009430home gateway helps overcome the problems of networkinteroperability. The home gateway in our implementationprovides interoperability between the local ZigBee and Wi-Finetworks and the Internet. Moreover the home gateway offersthe potential to be easily extended to include interoperabilityfor other communication standards. Furthermore, the homegateway unifies the interface offered by the system across thedifferent networks and devices used to access the system. Thefeasibility and appropriateness of the proposed architectureand technologies in the creation of a low cost, flexible andsecure system has been successfully evaluated both throughexperimentation and user trials. Experimentation hashighlighted the stability of the novel architecture adopted,including the minimal impact of the inclusion of the virtualhome on system’s performance. The potential for successfulco-existence and interoperability of Wi-Fi and ZigBee hasbeen practically proven with implementation with a real homeautomation system. Focus group sessions have shown apositive attitude towards the developed system and significantsupport for the diverse modes of control, monitoring, andintegration with existing home networks such as Wi-Fi.ACKNOWLEDGMENTThe authors wish to thank colleagues from the network andcontrol research group at Loughborough University for theircontinued support and feedback.REFERENCES[1] K. Bromley, M. Perry, and G. Webb. "Trends in Smart Home Systems,Connectivity and Services", www.nextwave.org.uk, 2003.[2] A. R. Al-Ali and M. Al-Rousan, "Java-based home automation system",IEEE Transactions on Consumer Electronics, vol. 50, no. 2, pp. 498-504, 2004.[3] N. Sriskanthan, F. Tan and A. Karande, "Bluetooth based homeautomation system", Microprocessors and Microsystems, Vol. 26, no. 6,pp. 281-289, 2002.[4] H. Ardam and I. Coskun, "A remote controller for home and officeappliances by telephone", IEEE Transactions on Consumer Electronics,vol. 44, no. 4, pp. 1291-1297, 1998.[5] T. Baudel and M. Beaudouin-Lafon, "Charade: remote control of objectsusing free-hand gestures", Communications of the ACM, vol. 36, no. 7,pp. 28-35, 1993.[6] T. Saito, I. Tomoda, Y. Takabatake, J. Ami and K. Teramoto, "HomeGateway Architecture And Its Implementation", IEEE InternationalConference on Consumer Electronics, pp. 194-195, 2000.[7] N. Kushiro, S. Suzuki, M. Nakata, H. Takahara and M. Inoue,"Integrated home gateway controller for home energy managementsystem", IEEE International Conference on Consumer Electronics, pp.386-387, 2003.[8] S. Ok and H. Park, "Implementation of initial provisioning function forhome gateway based on open service gateway initiative platform", The8th International Conference on Advanced Communication Technology,pp. 1517-1520, 2006.[9] D. Yoon, D. Bae, H. Ko and H. Kim, "Implementation of HomeGateway and GUI for Control the Home Appliance", The 9thInternational Conference on Advanced Communication Technology, pp.1583-1586, 2007.[10] K. Shuaib, M. Boulmalf, F. Sallabi and A. Lakas, "Co-existence ofZigbee and WLAN - a performance study", IFIP InternationalConference on Wireless and Optical Communications Networks, pp. 5,2006.[11] Jennic, "JN-AN-1059 Deployment guidelines for IEEE 802.15.4/ZigBeewireless networks", 37-38, 2007.Khusvinder Gill is a PhD student in the ComputerScience Department at Loughborough University. Hisresearch interests include security of remotecommunications, and wireless sensor networks. He is astudent member of the IEEE. He received his B.Sc.degree from Loughborough University, UK in 2006.Shuang-Hua Yang, Professor of Networks and Control,is the director of the Networks and Control ResearchGroup in the Computer Science Department atLoughborough University. He is also an overseasprofessor in Central China Normal University and a guestprofessor in Huazhong University of Science andTechnology, Petroleum University China, and LiaoningUniversity of Petroleum and Chemical Technology. His research interestsinclude wireless sensor networks, networked control, safety critical systems,and real time software maintenance. He is a fellow of the Institute ofMeasurement & Control (FInstMC), a senior member of IEEE (SMIEEE), anda Chartered Engineer (CEng) in the UK. He is an associate editor of theInternational Journal of Systems Science, and the International Journal ofAutomation and Computing. He is also serving as a member of the editorialadvisory board for the International Journal of Information and ComputerSecurity, Journal of Measurement and Control, International Journal ofAdvanced Mechatronic Systems, and International Journal of Process SystemEngineering. Professor Yang received his B.Sc. degree in instrument andautomation, M.Sc. degrees in process control from Petroleum UniversityChina in 1983 and 1986 respectively, and his Ph.D. degree in intelligentsystems from Zhejiang University in 1991.Fang Yao is a PhD student in the Computer ScienceDepartment at Loughborough University. His researchinterests include interference of wireless networks androuting protocols for wireless sensor networks. Hereceived his B.Sc. degree from Tianjin Science andTechnology University, China in 2003 and his M.Sc.degree from Loughborough University, UK in 2005.Xin Lu is a PhD student in the Computer ScienceDepartment at Loughborough University. His researchinterests include energy harvesting devices for ZigBeeelectronics. He received his B.Sc. degree from BeijingInstitute of Technology, China in 2004 and his M.Sc.degree from Loughborough University, UK in 2005.