6 IEEE TRANSACTIONS ON INFORMATION TECHNOLOGY IN BIOMEDICINE, VOL. 16, NO. 1, JANUARY 2012 A Reliable Transmission Protocol for ZigBee-Based Wireless Patient Monitoring Shyr-Kuen Chen, Tsair Kao, Chia-Tai Chan, Chih-Ning Huang, Chih-Yen Chiang, Chin-Yu Lai, Tse-Hua Tung, and Pi-Chung Wang Abstract—Patient monitoring systems are gaining their impor- tance as the fast-growing global elderly population increases de- mands for caretaking. These systems use wireless technologies to transmit vital signs for medical evaluation. In a multihop ZigBee network, the existing systems usually use broadcast or multicast schemes to increase the reliability of signals transmission; however, both the schemes lead to significantly higher network traffic and end-to-end transmission delay. In this paper, we present a reliable transmission protocol based on anycast routing for wireless pa- tient monitoring. Our scheme automatically selects the closest data receiver in an anycast group as a destination to reduce the trans- mission latency as well as the control overhead. The new protocol also shortens the latency of path recovery by initiating route recov- ery from the intermediate routers of the original path. On the basis of a reliable transmission scheme, we implement a ZigBee device for fall monitoring, which integrates fall detection, indoor position- ing, and ECG monitoring. When the triaxial accelerometer of the device detects a fall, the current position of the patient is transmit- ted to an emergency center through a ZigBee network. In order to clarify the situation of the fallen patient, 4-s ECG signals are also transmitted. Our transmission scheme ensures the successful transmission of these critical messages. The experimental results show that our scheme is fast and reliable. We also demonstrate that our devices can seamlessly integrate with the next generation tech- nology of wireless wide area network, worldwide interoperability for microwave access, to achieve real-time patient monitoring. Index Terms—Anycast, broadcast, ECG, multicast, patient monitoring, vital sign sensor, worldwide interoperability for mi- crowave access (WiMAX), ZigBee. Manuscript received October 1, 2010; revised April 19, 2011; accepted October 1, 2011. Date of publication October 13, 2011; date of current ver- sion February 3, 2012. This work is supported in part by the National Science Council under Grant NSC98-2218-E-241-004 and Grant NSC99-2221-E-005- 015. S.-K. Chen was with the Department of Computer Science and Engineer- ing, National Chung Hsing University, Taichung 402, Taiwan. He is now with Aerospace Industrial Development Co., Ltd., Taichung 40760, Taiwan. T. Kao is with the Department of Biomedical Engineering, Hungkuang Uni- versity, Taichung 43302, Taiwan. C.-T. Chan, C.-N. Huang, C.-Y. Chiang, and T.-H. Tung are with the De- partment of Biomedical Engineering, National Yang-Ming University, Taipei 11221, Taiwan. C.-Y. Lai was with the Department of Computer Science and Engineering, National Chung Hsing University, Taichung 40227, Taiwan. He is now with Gemtek Technology Co., Ltd., Hsinchu 30352, Taiwan. P.-C. Wang is with the Department of Computer Science and Engineering, Na- tional Chung Hsing University, Taichung 40227, Taiwan (corresponding author, e-mail: pcwang@cs.nchu.edu.tw). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TITB.2011.2171704 I. INTRODUCTION A CCORDING to Kinsella and He’s [1] report from the US Census Bureau, the global elderly population is fast growing and will outnumber the population of children in near future. The aging society is bringing its impact on many de- veloping countries and presents a stark contrast with the low fertility rate of these countries. The changes brought about by the aging society include an increasing demand for caretaking; thus, patient monitoring systems are gaining their importance in reducing the need for human resources. Caretaking homes and hospitals have been planning on the use of biological sen- sors to effectively minister to their patients. Vital signs, such as body temperature, blood pressure, and sugar level, can be regularly collected and remotely monitored by medical profes- sionals, achieving a comprehensive caretaking system. The transmission of vital signs in nursing homes and hos- pitals is usually carried out wirelessly. The vital signs can be categorized into emergency messages and regularly collected information. While the regularly collected information can be stored and transmitted in a given time period, the emergency messages must be transmitted immediately. The transmission path of vital signs can be divided into outdoor and indoor. The technology of wireless wide area networks (WWANs) is used for outdoor transmission, and that of wireless mesh network (WMN) is responsible for indoor transmission. Long term evolution (LTE) and worldwide interoperability for microwave access (WiMAX) are the next generation technolo- gies for WWAN. Both technologies aim at providing wireless broadband access service and have the same core wireless tech- nologies, but in different manner. While the technology of LTE considers incumbent deployments, which pursue compatibility with the existing devices, WiMAX is primarily used in fixed to mobile deployments. These technologies will greatly improve the quality of patient monitoring since the vital signs can be transmitted with better bandwidth management. For the indoor transmission of vital signs, WMN is a conve- nient technology, which can dynamically establish a multihop network topology without prior configuration. The WMN de- vices could change locations and configure itself on the fly. They are also widely adopted for indoor positioning [2]–[5]. These devices have advantages of power efficiency, low cost, and small volume and size. ZigBee [6] is an open standard technology to address the demands of low-cost, low-power WMNs via short- range radio. ZigBee is targeted at RF applications that require a low data rate, long battery life, and secure networking. Its mesh networking also provides high reliability and more extensive range. The ZigBee devices can be combined with WWANs to 1089-7771/$26.00 © 2011 IEEE