An Integrated ZigBee Automation System: An Energy Saving Solution

Transcription

1 An Integrated ZigBee Automation System: An Energy Saving Solution KF Tsang, WC Lee, KL Lam, HY Tung and Kai Xuan Abstract ZigBee is the latest wireless technology which provides three lowest solutions, low data rate, low power consumption and low cost. One of the ultimate goals of ZigBee is to provide a energy saving solution. Low power consumption and power management are important characteristics of ZigBee. To explore the concept of energy saving, an integrated ZigBee Automation System (ZAS) for lighting automation and power management is investigated. In this paper, the details of system design for ZAS are described including the system overview, deployment as well as the power management algorithms. Index Terms ZigBee, Energy saving, Power management, Automation I. INTRODUCTION ZigBee is a standard providing specifications for communication protocols of the network layer based on the IEEE standard for wireless personal area networks (WPANs) [3]. The protocols are intended for use in embedded applications requiring low data rates and low power consumption [5]. ZigBee is developed for networking control and sensor nodes because a network node can be built for a few pounds using a single-chip radio and a microcontroller. The standard also supports ad hoc mesh networking, in which separate nodes forma network by discovering each other s presence over the air. Messages are then passed from node to node until the signals arrive at the right destination. Hence no special expertise is needed to build a ZigBee network simply place sufficient nodes within radio range of each other and the network forms. Moreover, there are multiple routing paths from source node to destination node. When one node fails, messages are routed around the blockage rather than being simply dumped. Attributed to the captioned characteristics, the technology of ZigBee represents a wireless network which is highly reliable, networking, secure, low data-rate, low power consumption, low costs, and fast reaction. ZigBee makes it possible to design easy-to-in 1 stall network kits (especially good for home usage) and the network capability assures room for further network expansion to cater for future 1 This work was supported in part by the Freescale Semiconductor Ltd and Citycom Technology Limited KF Tsang, WC Lee, KL Lam, HY Tung and Kai Xuan with Department of Electronic Engineering, City University of Hong Kong, 83 Tat Chee Avenue, Kowloon Tong, Hong Kong, SAR China (corresponding ee330015@cityu.edu.hk, @student.cityu.edu.hk, kalunlam@student.cityu.edu.hk, hytung@student.cityu.edu.hk, xuankai@student.cityu.edu.hk) ZigBee deployment. All the factors accommodate ZigBee to be the ideal technology implemented into the fields of home automation. For illustration purpose, the home control light switch profile is used as the reference. In this paper, an integrated ZigBee Automation System (ZAS) is proposed. The remaining session of this paper is organized as follows. The system overview of ZAS is presented in Section II. Section III gives the details in deployment of ZAS while the power management scheme is discussed in section IV. Finally, a conclusion is drawn in section V. Fig 1 ZAS system II. SYSTEM OVERVIEW OF ZAS Fig 1 shows an overview of ZigBee Automation System (ZAS). One ZigBee Remote Controller (ZRC) can be in charge of the operation of all the home appliances such as lights, computer, TV, air conditioner, wash machine, microwave oven, etc. Usually the electronic appliances scatters in different rooms of an apartment and users expect to control all the scattered devices in a certain room. In the ZAS, users simply controls ZigBee signal by using a remote controller from which signals can reach any room wirelessly. As shown in Fig 1, ZRC in room B can switch on/off all the home electronic appliances listed in the bottom of Fig.1. Packet length of signal in proposed ZAS is with maximum length of 17 bytes including header and 16-bit checksum (CRC), where the payload is up to 104 bytes. Some channels have duty cycle restriction or recommendation to achieve minimum conflicts among different ZigBee networks. The IEEE employs optional acknowledgement mechanism to provide acknowledged transmissions if needed. However the acknowledgement is on the MAC layer only. The ZigBee stack or the application has to take care that all data received

2 by the MAC layer will be processed. The acknowledgement mechanism takes care of repeated transmission if acknowledgment is not received within a defined time. If data fragmentation will occur in the data transmission further checksum Based on IEEE PHY/MAC[3], the ZigBee network layer provides functionality such as dynamic network formation, addressing, routing, and discovering 1 hop neighbors. Since the size of the network address is 16 bits, one ZigBee network is capable to accept about devices maximally. The number of devices under control of ZAS shown in Fig 1 is far below ZigBee s capability. Network address is assigned in a hierarchical tree structure. The deployed ZigBee devices automatically construct the network, and then changes such as joining/leaving of devices are automatically reflected in the network configuration. ZRC and all the home electronic appliances in ZAS can be considered as ZigBee nodes. ZigBee provides two routing protocols for finding path from source node to destination node: table-driven routing and tree routing. Table driven routing is basically similar to the Ad hoc Ondemand. Tree routing is based on the block address allocation mechanism, called Cskip, so each device has an address spaces to distribute to their children. Tree routing is employed in ZAS system because of its simplicity and limited use of resources[6]. When a device has no capability of routing table and route discovery table, it simply follows the hierarchical tree by comparing the destination address. Application profile-- home automation is built upon the network layer In one ZAS, three kinds of ZigBee devices can be configured: one network coordinator, which maintains overall network knowledge. It is the most sophisticated of the three types and requires the most memory and computing power; the full function device (FFD), which can function as a network coordinator with additional memory and computing power and is ideal for network router functions or it could be used in network-edge devices; the reduced function device (RFD), carring limited functionality to lower cost and complexity and is generally found in network-edge devices [4]. As mentioned at the beginning of this section, all the electronic home appliances scattering in different rooms are controlled by one ZRC, it is important to acknowledge the user about the status of each device under control. Fig. shows the on/off status of the electronic devices. The status is displayed on the screen embedded in ZRC. Star shape represents the device s location while circle shape indicates the current device shows up in that certain location. Blank star is a symbol for off status and filled star is the sign of on status. By monitoring the display in Fig., user holding ZRC is acknowledged the on/off status of all the electronic appliances in the apartment. Virtually all devices in ZAS system can be remotely controlled. Fig. Display of on/off Status With the proposed ZAS, electronic devices are effectively controlled remotely. Device is going to be switched off right after there is no need for it because it is easy for users to notice the on/off status of the entire system. Such that, wasting power is reduced. Further more, a power management scheme is proposed for ZAS which would be described in section IV. III. THE DEPLOYMENT OF ZAS In a ZigBee system, the specifications allow three kinds of device within the system: ZigBee Coordinator (ZC) - a Full Function Device (FFD), ZigBee Router (ZR) also a FFD, and ZigBee End-Device (ZED) a Reduce Function Device (RFD). The ZC is the most capable device which forms the root of the network. There is exactly one ZC in each network and it is responsible to initialize the network configuration, such as channel selection, PANID selection, etc. The ZR acts as an intermediate router, relaying data from other devices, and allows the network to be operated as a tree or mesh topology. The ZED contains just enough functionality to talk to its parent node (either the coordinator or a router). In our system, the ZigBee Coordinator functionary is applied to a light switch application, the ZigBee Router functionary is applied to light switch application or power socket application, and a modified ZigBee FFD functionary is applied to a handheld remote controller. The Light Switch of ZigBee Coordinator (LSC) is the unique device in our system to initialize the network and manage the system operation. The Light Switch of ZigBee Router (LSR) or the Power Socket of ZigBee Router (PSR) is used to extend the system coverage. ZRC is used to control the light and power socket remotely (Fig. 3).

3 Fig.3 The devices for ZAS The modified ZigBee FFD (MFFD) is specially designed for battery powered remote controller applications. During operation, the MFFD is equipped with router capability, implying that the remote controller is able to send route requests to locate a light switch or power socket in the system. In our system, there is no need that the MFFD has to be attached with a ZR as the parent for network access, hence the device is mobile. On the other hand, the MFFD will enter into the power saving mode to reduce the battery power consumption, which is similar to the function of a RFD. The circuit design of ZigBee device can be found in Fig 4- Fig 9. Fig 5 Remote main broad schematic Fig.4 Block diagram of ZigBee device circuit design Fig 6 Remote main broad schematic

4 Fig 7 Remote RF broad schematic Fig. 8 Switch Power broad schematic Fig. 9 Switch RF broad schematic SIMPLIFIED CONFIGURATION PROCEDURE A. Network Initialization In the initialization of network, the user initially turns on the LSC, and then press an init button to instruct the coordinator to initialize network automatically. When the user presses the init button, the LSC will first perform Energy Density (ED) scan and active scan to identify any ZigBee network within coverage. The LSC will then select a clear channel and a PANID for the network establishment. On the user level, they are not required to understand any step of LSC operations, only the init button is used for the initialization of the network. B. Join Device After the network has been initialized, the network is preconfigured as a private network and it does not allow any ZigBee device to join without the permission from the enduser. This pre-configuration is important since by doing so, different ZigBee systems are separated to avoid interference during the network joining of a new device. When an end-user has desired to add a new device (LSR, PSR or ZRC) to the network, the user shall press a permit join button on the LSC, and then press a join button on the new device to permit the device joining the network. Once the permit join button on the LSC is pressed, the LSC will broadcast a permit join message in the network to allow all LSRs and PSRs to accept device joining. When the join button of a device is pressed, the device will

5 perform active scan and association procedures compiling to the ZigBee specifications. After the device has joined the network successfully, its parent will broadcast a join completed message in the network to inform all the network members that a new device has joined, and the other network members will stop accepting any join request. C. Binding According to the ZigBee specifications, there is a binding procedure to match a ZigBee device input end-point, which is a control button, to one or multiple ZigBee device output endpoint(s), which is/are the device load(s). Our system allows the user to map to any output end-point of any ZigBee compatible device to the control buttons of the ZRC. In other words, the user may set a button on the ZRC to control a single or a group of devices. For example, the user may match a light switch in the living room, a light switch in the bed room, or a power socket in the bed room to a single button on the ZRC. The user is then able to press a single button to switch on/off multiple devices. When a user desires to bind a ZigBee output end-point to the remote controller, the user may switch the target device (LSC, LSR or PSR) from normal operation mode to binding mode, and then press the control button on the device, which is related to the target output end-point. This procedure will instruct the target device to send a binding request to the ZC. The user then enters the add device menu of the ZRC to attach the target end-point to the control button, where the ZRC will also send a binding request to the ZC. After the ZC has matched the output end-point with the input endpoint, it will send the binding record to the ZRC and the ZRC will store the record to the non-violate memory for further control operation. Power consumption is one majority source of air pollution. ZAS with the novel power control system will help users to cut off the unnecessary usage of home appliance. Power expense of a family is reduced with the less electricity consumption and eventually, the air of the entire society is improve as electricity consumption is one of the major source of air pollution. In the proposed algorithm, distribution of power consumption per day is adjusted according to variable charge fee by the electricity operator. And overspending is avoided by checking the accumulated power consumption is checked every five days. Flow chart of the proposed control algorithm is as show in Fig 10 The power consumption charge is variable in different time zones in a day for regions such as Mainland China. The reason is that all users have similar power usage habit, which directly cause the power consumption peaks, for example, dinner time is one the peaks as family members are cooking, doing laundry, watching TV, ironing with air conditioner being turned on. The consumption peak is not a pleasant situation for electricity operators because they need to control the operating cost while meeting the customers requirements. Fig 11 shows the power charge scheme in different time zone. It is seen that the price of power per degree consumption is especially higher than some other time period. It is seen that higher fee will be charged at the potential consumption peak. IV. THE POWER MANAGEMENT SCHEME Fig 11 Power charge scheme in different time period(per day) Fig 10 Flow chart of the proposed power management scheme The power charging scheme can also be expressed in equ. (1) pt1 ; 0 t < t1 equ. (1) pt ; t1 t < t pt ( t) = pt 3 ; t t < t3

6 p i is the fee per degree charged by the electricity operator for time period from t i 1 to t i. Besides, charge of power fee is also variable with the power degree which has been used because of environment protection consideration. The power charge per degree rises for a certain user when the accumulated power consumption exceeds a defined range. Fig 1 illustrates the charging scheme of electricity operator. It is seen that customers pay higher bill for environmental issue when more power are generated. Where d the accumulated power consumption for one month. Fig 13 shows a sample of original power consumption distribution v (t). From Equ. (1), power charge the user should pay for one day is: equ. (3) C = p ( t) v( t) dt per day t v(t) is the power consumption function which is variable with time t. equ. (4) v ( t) = v j ( t) j And the power consumption per month is d v( t) dtdm equ. (5) = m, t Where m represents the days in one month T Considering Equ. () and (3), the total power expense for one month is: C per month = Cm + pv (d) equ. (6) m Fig 1 Power charge scheme at different consumed power(per month) Fig 14 Modified power consumption distribution Fig 13Original power consumption distribution This power charging scheme according to the accumulated power consumption is expressed in Equ. () pv1 ; 0 d < d1 equ. () pv ; d1 d < d pv ( d) = pv 3 ; d d < d 3 To control the expense of power fee per month-- C per month expressed in Equ. (5), the consumption contribution in every day should be adjusted and the accumulated power during one month will be modified accordingly. Obviously, the power consumption in Fig 11 is high when the price charge is expensive. In the proposed algorithm, some schemes are developed to reduce the power expense by moving forward the peak of curve in Fig. 13 at the time when the price is lower. The recommended power consumption scheme is shown in Fig. 14 If the user chooses the recommended scheme, the wireless control system will automatically switch off some home appliances in the peak

7 time (as Fig 11 shows). In this way, configured/controlled to be low. Cm in Equ. (5) can be Moreover, the degree of power consumption should be monitored because more fee will be charged with higher accumulated power(see Fig 10). In order to control the element p V (d) in Equ.(5) to be a low value, d shall be controlled in an expected range (refer to Equ.(). In the proposed algorithm, once a family sets a target power consumption value for one month, the power consumption per five days are planned. If the realistic consumed power exceeds the planned value, which is checked every five days, the consumption plan will be modified for the following day and warning information is notified to the customers. In this way, customers are aware of the overspending and take the advices of the modified plan from the proposed algorithm. [7] Masahiro Inoue, Toshiyasu Higuma, Yoshiaki Ito,Noriyuki Kushiro, Hitoshi Kubota, Network Architecture for Home Energy Management System, IEEE Trans. Consumer Electron., vol. 49, no.3, pp , Aug. 003 [8] D.S. Kim, J.M. Lee, W.H. Kwon, I.K. Yuh, Design and implementation of home network systems using UPnP middleware for networked appliances, IEEE Trans. Consumer Electron., vol. 48, Issue 4, pp , Nov 00. V. CONCLUSION A ZigBee Automation System (ZAS) is developed. The developed system is low cost and robust and fully takes the advantages of ZigBee. A ZigBee Remote Controller(ZRC) is designed, with which, on/off status of all the devices can be viewed. A power management scheme for ZAS is proposed. The intelligent algorithm considers usage habit of customers and the economic effect. With the proposed algorithm, the distribution of power consumption per day is adjusted so that the daily expense is reduced. In the scheme, the accumulated power consumption is checked every five days to avoid overspending. By adopting the consumption plan generated by the proposed algorithm, the unnecessary power consumption is reduced or even cut off. As a result, power consumption per family is much reduced. ACKNOWLEDGEMENT The assistance from Freescale Semiconductor Ltd. and sponsorship from Citycom Technology Ltd. are gratefully acknowledged. REFERENCES [1] Ryan, J.L., Home automation, Electronics & Communication Engineering Journal, Volume 1, Issue 4, July-Aug Page(s): [] Ondrej, S.,Zdenek, B., Petr, F., Ondrej, H., ZigBee Technology and Device Design, Networking, International Conference on Systems and International Conference on Mobile Communications and Learning Technologies, 006, Page(s):19 19 [3] IEEE Std : Wireless Medium Access Control (MAC) and Physical Layer (PHY) Specifications for Low-Rate Wireless Personal Area Networks (LR-WPANs), 003 [4] ZigBee Alliance Document 0130rlO: Network Layer Specification,December 14th, 004. [5] Egan, D., "The emergence of ZigBee in building automation and industrial control", IEEE Journal of Computing & Control Engineering 005. [6] Taehong Kim; Daeyoung Kim; Noseong Park; Seong-eun Yoo; Lopez, T.S., Shortcut Tree Routing in ZigBee Networks, Wireless Pervasive Computing, 007. ISWPC '07. nd International Symposium on 5-7 Feb. 007