IEEE Communications Magazine December - PDF document

OMMUNICATIONSAND Huasong Cao and Victor Leung, University of British ColumbiaCupid Chow and Henry Chan, The Hong Kong Polytechnic University Enabling Technologies for Wireless Body IEEE Communications Magazine ¥ December 2009 89 certified wireless USBdevices work at up to 480Mb/s, enabling short-range wireless multimediaapplications, such as wireless monitors, wirelessAn emerging WBAN standard, IEEE 802.15.6Ñ Body Area Networks (BANs), will likelyBLUETOOTH3.0 + HIGHSPEEDBluetooth technology was designed as a replace-Limitations of Bluetooth include the smallnumber of active slaves (seven) that each piconetZIGBEEZigBee/IEEE 802.15.4 targets low-data-rate andTable 2.A comparison of WBAN and WPAN technologies. (Only most commonly acknowledged and/or applied parameters are listedhere due to space limitation.) Technology Frequency band Data rate (b/s) Multiple access method Coverage area(meter) Network Bluetooth Low Energy 2.4 GHz ISM 1 M FH + TDMA 10 Star UWB (ECMA-368) 3.1~10.6 GHz 480 M CSMA/TDMA Star Bluetooth 3.0 + Highp 2.4 GHz ISM 3~24 M FH + TDMA/CSMA (Wi-Fi) 10 star ZigBee (IEEE 802.15.4) ISM 250 k CSMA 30~100 Star/mesh Insteon 131.65 KHzp 13 k Unknown Home area Mesh Z-Wave 900 MHz ISM 9.6 k Unknown 30 Mesh ANT 2.4 GHz ISM 1 M TDMA Local area Star/mesh RuBee (IEEE 1902.1) 131 KHz 9.6 k unknown 30 Peer-to- RFID (ISO/IEC 18000-6) 860~960 MHz 10~100 k Slotted-Aloha/binary tree 1~100 Peer-to- FH: Frequency hoppingTDMA: Time-division multiCSMA: Carrier sense multip CHAN LAYOUT 11/18/09 2:02 PM Page 89 IEEE Communications Magazine ¥ December 2009 88 multiple-standard radios can be integrated into asingle chip, greatly reducing the cost and powerBLUETOOTHLOWENERGYTECHNOLOGYBluetooth Low Energy technology, formerlyhardware-optimizedradio, which means itsmajor difference from Bluetooth resides in theBluetooth Low Energy technology is expectedto provide a data rate of up to 1 Mb/s. Usingtion and emergency response) and enhancesSimilar to Bluetooth, Bluetooth Low Energytechnology will likely operate using a simplerUWBAccording to the Federal Communications Com-Figure 2.Typical modules on a sensor node. Sensor node Sensor node Sensor node Bus Data flow Sensor node WBAN RAM: Random access memoryROM: Read-only memoryRadio module WPAN Senso ADC Sensor module Filter RAM Flash Memory module ROM Microprocessor Bluetooth LEE wasdesigned to wirelessly connectsmall devices tomobile terminals.Those devices areoften too tiny tobear the power consumption as wellas cost associatedwith a standardBluetooth radio, butare ideal choices forhealth-monitoringapplications. CHAN LAYOUT 11/18/09 2:02 PM Page 88 IEEE Communications Magazine ¥ December 2009 84 0163-6804/09/$25.00 © 2009 IEEE 1There is no strict differ-ence between WBAN andWPAN in their defini- INTRODUCTIONWith the growing needs in ubiquitous communi-cations and recent advances in very-low-power CHAN LAYOUT 11/18/09 2:02 PM Page 84 IEEE Communications Magazine ¥ December 2009 93 [7] E. Farella et al., “Interfacing Human and Computer withWireless Body Area Sensor Networks: The WiMoCASolution,” Multimedia Tools App., vol. 38, no. 3, July2008, pp. 337–63.[8] P. J. Xu, H. Zhang, and X. M. Tao, “Textile-StructuredElectrodes for Electrocardiogram,” Textile Progress, vol.40, no. 4, Dec. 2008, pp. 183–213.[9] P. S. Hall and Y. Hao, Antennas and Propagation forBody-Centric Wireless Communications, Artech House,2006.[10] K. Y. Yazdandoost et al., “Channel Model for BodyArea Network (BAN),” IEEE P802.15-08-0780-08-0006,pr. 2009.[11] K. Takizawa, T. Aoyagi, and R. Kohno, “Channel Mod-eling and Performance Evaluation of UWB-based Wire-Proc. IEEE ICC 2009,Dresden, Germany, 2009.[12] R. Istepanian, S. Laxminarayan, and C. S. Pattichis, M-Health: Emerging Mobile Health Systems, Springer,2005.[13] M. C. Munshi et al., “Wireless ECG Plaster for BodySensor Network,” Proc. 5th IntÕl. Wksp. Wearable and., Hong Kong, China,2008.[14] Y. P. Zhang, L. Bin, and C. Qi, “Characterization of On-Human-Body UWB Radio Propagation Channel,”Microwave Optical Tech. Lett., vol. 49, no. 6, pp1365–71.[15] J.-Y. Yu, W.-C. Liao, and C.-Y. Lee, “A MT-CDMA basedWireless Body Area Network for Ubiquitous HealthcareProc. BioCAS 2006pp98–101.[16] A. Kurs et al., “Wireless Power Transfer via StronglyCouled Magnetic Resonances,” Science, vol. 317, no.5834, July 2007, pp. 83–86.[17] S. Warren and E. Jovanov, “The Need for Rules ofEngagement Applied to Wireless Body Area Networks,”Proc. IEEE CCNC 2006, Las Vegas, NV, 2006.BIOGRAPHIESHUASONGCAO[S] (huasongc@ece.ubc.ca) received hisB.Eng. degree in electrical engineering from Wuhan Univer-puter engineering at the Uni-versity of British Columbia. His research interests includepecifically wireless bodyarea networks.CUPIDCHOW(cscschow@com.polyu.edu.hk) is a laboratoryofficer at the Department of Computing, The Hong KongPolytechnic University. She received her M.A.Sc. degree inelectrical engineering from the University of Britishp the adap-tive modulation and coding (AMC) scheme for high-speeddownlink Packet Access (HSDPA). She has been working onHENRYC. B. CHAN[M] (cshchan@comp.polyu.edu.hk)received his B.A. and M.A. degrees from the University ofCambridge, England, and his Ph.D. degree from the Univer-profes-sor in the Department of Computing, The Hong KongPolytechnic University. His research interests include net-VICTORC. M. LEUNG[F] (vleung@ece.ubc.ca) received hisB.A.Sc. and Ph.D. degrees, both in electrical engineering,from the University of British Columbia in 1977 and 1981,ectively. He is a professor and holder of the TELUSMobility Research Chair in the Department of Electrical andComuter Engineering of the same university. His researchinterests are in wireless networks and mobile systems. HeIEEE Transactions on Computers. Wireless Engineering Professionals(WEBOK)www.wiley.comUS $69.95IEEE Communications 15% discount with Promo Code: 18493+1 877 762 2974 (US) +1 800 567 4797 (Canada) +1 44 1243 843294 (world)ISBN: 978-0-470-43366-9Paper, 272pp, 2009 WCET Area 2:Technologies WCET Area 3: Network and Service by Daniel Wongwww.comsoc.org/tutorialsnow IEEEWCETCerti“cation Program www.ieee-wcet.org CHAN LAYOUT 11/18/09 2:02 PM Page 93 ABSTRACTA wireless body area network is a radio-fre-quency-based wireless networking technology IEEE Communications Magazine ¥ December 2009 87 ECHNOLOGIESOGIESfrequency bands, intra-body, on-body, and off-body channels have been studied. Figure 3 showsan example of the path loss measurements forseveral body locations and frequency bandsbased on [10]. The intra-body propagation chan-nel can be described using an appropriate model.For example, the Ricean distribution can beused for modeling the intra-body propagationchannel based on the K-factor, which is the ratiobetween the average powers of the direct andreflected paths [4], and indicates the channelquality. Significant progress has also been madetoward:¥Identification of the propagation mecha-¥Assessment of the effects of multipath¥Characterization of the fading statistics on¥Development of standard UWB channel Sensor How it works Data rate Accelerometer Measures the acceleration relative to freefall in three axes High Gyroscoe Measures the orientation, based on the p High ECG/EEG/EMG Measures High Pulse oximetry Measures ratio of changing absorbance of the red and infrared light pother of a thin Low Res Uses two electrodes, cathode and anode covered by a thin membrane to measure the oxygen dis-solved in a liquid Low Carbon dioxide Uses the infrared light and measures the absorpp Low Blood Measures the systolic Low Blood sugar Traditionally analyzes dropp Low Humidity Measures the conductivity changes of the level of humidity Very low Tem Uses a silicon integrated circuit to detect the temp Very low CHAN LAYOUT 11/18/09 2:02 PM Page 87 IEEE Communications Magazine ¥ December 2009 91 SSUESHARACTERISTICSOFATERIALSANDEVELOPMENTANDVALUATIONOFROPAGATIONAND WBANsWBANsWBANsWBANs Link to other networksMetropolitan area WBANs CHAN LAYOUT 11/18/09 2:02 PM Page 91 IEEE Communications Magazine ¥ December 2009 85 PPLICATIONSOFSFORFORtiple router nodes can be deployed on the wall.All nodes use the same ZigBee radio.Patients/caregivers can publish/subscribe to themesh network by multicasting; there is no cen-tralized or distributed server or database forcontrol and storage. Localization functionality isprovided by MoteTrack with an accuracy of 1 m,based on the same radio. As a result of mobilityand multihop transmissions, the system experi-ences considerable packet loss and is limited to40 kb/s aggregate bandwidth per receiver.Based on the CodeBlue architecture, theAdvanced Health and Disaster Aid Network(AID-N) is being developed at Johns HopkinsUniversity [2] for mass casualty incidents whereelectronic triage tags can be deployed on victims.Additional wireless capabilities (e.g., Wi-Fi andcellular networks) are introduced to facilitatecommunications between personal servers andthe central server where data are stored. Fur-thermore, a web portal is provided to multipletypes of users, including emergency departmentpersonnel, incident commanders, and medicalspecialists. A Global Positioning System (GPS)module is employed for outdoor localization,while a MoteTrack system is designed for track-ing indoors. However, patients have mobilityconstraints due to the lack of routers in the net-work, and a very limited number of sensor nodescan be put on each patient because of the limit-ed bandwidth.The Wearable Health Monitoring Systems(WHMS) is being developed at the University ofAlabama [3] and targets a larger-scaletelemedicine system for ambulatory health statusmonitoring. Unlike CodeBlue and AID-N,WHMS has a star-topology network for eachpatient, which is connected via Wi-Fi or a cellu-lar network to a healthcare provider. The per-sonal server, implemented on a personal digitalassistant (PDA), cell phone, or personal comput-er (PC), coordinates the data collection fromsensor nodes using a time-division multipleaccess (TDMA) mechanism, provides an inter-face to users, and transfers data to a remote cen-tral server. Physicians can access data via theInternet, and alerts can be created by an agentrunning on the server. However, the power con-sumption and cost associated with long-termdata uploading can hamper system realization.WBANSFOR WPANTo InternetTo WMANWatch CHAN LAYOUT 11/18/09 2:02 PM Page 85 types mentioned earlier, however, are based onIEEE 802.15.4 chips that do not employ thehigher-layer ZigBee protocol stack, becauseeither networking capability is not a must, orresearchers are interested in devising moreappropriate protocols. In our view, ZigBee mayhave a better chance to be adopted in the areaof home automation and industrial automationand control, while in the area of connectinglow-power peripheral devices around thehuman body (e.g., watches, health-related mon-itors, and sports sensors), Bluetooth Low Ener-gy technology has greater potential to be widelyemployed, due to its association with Bluetoothas well as lower cost and lower power con-sumption.CONNECTINGWBANSANDTHE IEEE Communications Magazine ¥ December 2009 90Figure 3.Path loss values for different body locations and frequency bands (based on [10]). Path loss in dB 0 Rightwrist Leftwrist Rightankle Leftankle Back(Receiver at right hip) 20 30 40 50 60 40 80 Path loss in dB 0 (Transmitter at left waist) Rightear Leftwrist Rightwrist Rightwaist Leftankle Rightankle 30 20 40 50 60 70 80 90 Path loss in dB 0 Rightwrist Leftwrist Rightankle Leftankle Back(Receiver at right hip) 20 30 40 50 60 40 80 Path loss in dB 0 (Transmitter at left waist) Rightear Leftwrist Rightwrist Rightwaist Leftankle Rightankle 30 20 40 50 60 70 80 90 Walking Standing Walking Standing CHAN LAYOUT 11/18/09 2:02 PM Page 90 IEEE Communications Magazine ¥ December 2009 92 human body over 3.1Ð10.6 GHz in the indoorand anechoic chamber to study the path lossexponent under various conditions. Anotherrelated issue is performance evaluation. Forexample, when the WBAN signal is transmittedbetween two sensors, the signal propagationthrough the body is affected by the diffractionaround the body and the reflections from thebody or other objects. Path loss and delayspread will affect the performance of the sys-tem, especially when the sensors are placed ondifferent sides of a body. According to onestudy, the packet error rate should generally bekept less than 1 percent [15].NETWORKINGANDANDRULESOFOF)gent monitoring and treatment systems employ-ing WBANs require standardized rules ofengagement in ambulatory environments, pro-viding point of care without limitation of thewearerÕs location/mobility while protecting thepatientÕs privacy. Interoperability protocols atthe application or domain level (e.g., samplerate, data precision, association/disassociation,device descriptions, and nomenclature) shouldall be addressed, and vendor-independentattributes and user interfaces shall be madeavailable. CONCLUSION While WBAN technologies providea promising platformto enable ubiquitouscommunications,several open issuesstill need to beaddressed. In particular, forthose life-savingapplications, thorough studies andtests should be conducted beforeWBANs can bewidely applied tohumans. CHAN LAYOUT 11/18/09 2:02 PM Page 92 IEEE Communications Magazine ¥ December 2009 86 of automatically recognizing human motions,gestures, and activities. Disabled people canEarly research efforts at MIT Media Labhave produced MITHril [5], a wearable comput-The Microsystems Platform for Mobile Ser-vices and Applications (MIMOSA) [6] is aThe Wireless Sensor Node for a Motion Cap-ture System with Accelerometers (WiMoCA) [7]SENSORDEVICESSensors are the key components of a WBAN, asa low sampling frequency and low data transmis-2), blood pres-sure, blood sugar, humidity, and temperatureAccelerometers are widely used for motioncapture. They measure the acceleration relativeECG/EMG/EEG sensors measure potentialdifferences across electrodes attached to corre-With advances in micro-electromechanicalsystems (MEMS), sensor devices are getting Traditional computerinterfaces, like keyboards, mice, joysticks, and touchscreens are allreplaceable bypotential WBANdevices capable ofautomatically recognizing humanmotions, gestures,and activities. Dis-abled people canbenefit from novelWBAN platformsbased on a series ofminiature sensors. CHAN LAYOUT 11/18/09 2:02 PM Page 86