PIERS ONLINE, VOL. 5, NO. 4, 2009 321 Invesigaion of Novel Ulrasonic Posiioning Mehod Insalled in Sensor Nework Misuaka Hikia, Yasushi Hiraizumi, Hiroaki Aoki, Junji Masuda, and Tomoaki Waanabe Faculy of Global Engineering, Kogakuin Universiy, Shinjuku-ku, Tokyo 163-8677, Japan Absrac A new concep called Sensor Nework has been proposed wih he developmen of mobile communicaions sysem such as cellular phone, radio LAN and Blueooh. Signals from many sensor nodes spread in a wide area are gahered o a cener node by echnology similar o ha used in mobile communicaions. Sensor nework enables home/office circumsance conrol, environmen monioring and proecion based on he colleced daa. We proposed a novel ulrasonic posiioning mehod which can be insalled in sensor nework. This mehod has also been invesigaed o be combined wih 2.4-GHz ZigBee, which has been regulaed by IEEE 802.15.4 as wireless-communicaions medium for sensor nework. 1. INTRODUCTION Cellular-phone sysems have spread all over he world and heir echnologies coninue o be developed during he firs half of he weny-firs cenury. On he oher hand ousanding echnical innovaions have been observed in a sensor area. A new concep called Sensor Nework has been proposed recenly by combining sensor echnologies wih such mobile communicaions sysem as cellular-phone, radio LAN and Blueooh. In his nework sysem, a lo of sensors disribued in a cerain area such as home, office and public places are conneced via raher simple privae radio communicaions nework. I is hough o have a big impac on our lives and o grow o be a gian indusry like he cellular-phone sysems. I will also conribue o fuure ecology, i.e., energy saving and environmenal preservaion. In our laboraory, we have been sudying he sensor nework o achieve comforable living circumsances by home/office sensing and conrol [1]. In his paper, we proposed a new ulrasonic posiioning mehod which can be insalled in he sensor nework. Sensor nodes require long-erm operaion wih eremely low-power supply, such as several-year operaion wih a single baery. However, such convenional ulrasonic posiioning mehods as a pulse-echo mehod and a code-division [2] mehod require high volage handling capabiliy for he ransmier and complicaed signal processing procedures for receiver, respecively. Therefore, heir devices can no be included in sensor nodes. Our proposed mehod can provide no only he low-power consumpion bu also removal of he complicaed signal processing procedures, which overcomes he limiaion for use as sensor-node devices [3]. Our mehod has also been invened based on ZigBee-based sensor nework. ZigBee has been regulaed by IEEE802.15.4 [4] and ZigBee Alliance as a wireless-communicaion medium used in low-power and long-erm radio sysems such as sensor nework. We also showed he feasibiliy of he new mehod by fundamenal eperimens compared wih hose of convenional mehod. The sensor nework including our posiioning devices will possibly be applied no only o home/office monioring bu also o care for old people, prevenion of crime and wach in hospials. 2. SENSOR NETWORK BASED ON ZIGBEE Teas Insrumen, one of he mos leading semiconducor-ic manufacuring companies, has a vision as shown in Fig. 1 for ZigBee-based sensor nework. Almos all office/home conrols, i.e., ligh, emperaure/humidiy, securiy/alarm, smoke-deecion/alarm and oher noificaions, are conduced via sensor nework. T. I. has a plan o provide semiconducor ICs used in such nework sysems. Our proposed ulrasonic posiioning devices will be insalled in sensor nodes ogeher wih hese developed ICs. ZigBee has been regulaed by IEEE802.15.4 [4] and ZigBee Alliance as a wireless-communicaion medium for he sensor nework. Wireless specificaions for ZigBee are shown in Table 1 compared wih oher recen radio communicaions media, i.e., Blueooh and UWB 2.4 GHz, same frequency as Blueooh, is used, bu daa rae is 250 Kbps which is abou one hird of Blueooh. The number of connecable nodes per one nework is 65,535, which is compleely differen from Blueooh s 7
PIERS ONLINE, VOL. 5, NO. 4, 2009 322 slaves per one maser pico-nework. Because of hese characerisics, sensor-nework is he mos adequae applicaion for ZigBee. The proocol srucure for ZigBee is shown in Fig. 2, which has almos same layer configuraion as Blueooh or oher radio communicaions sysems. The nework opology is shown in Fig. 3. No only convenional sar-link ype opology for Blueooh and radio LAN bu also new mesh-link ype and ree-ype opology can be possible for ZigBee, which can achieve 65,535 nodes conneced per one nework. Oher one of he mos imporan feaures required for ZigBee is he eremely low-power consumpion, which provide several-year operaion wih a single baery. Smoke Deecor & Alarm Radiaor & Air Condiioner Nework Monior Securiy & Alarm Lock/Unlock Door Conrol Ligh Sensor & Conrol Auomaic Noificaion Window & Blind Conrol Temperaure & Humidiy Sensor Remoe Conrol (Nework forwards messages) Figure 1: Concep of ZigBee-based sensor nework (slighly modified from originals in H. P. of T. I.). Table 1: Wireless specificaions for ZigBee, Blueooh and UWB. Sysem Frequency Modulaion Oupu Daa Rae Number of Nodes Applicaion ZigBee (IEEE802.15.4) 2.4 GHz OQPSK/DSSS 0 dbm 250 Kbps 65,535 Nodes /1 Nework Sensor nework Home nework Temperaure /Ligh/Air con. Securiy Blueooh UWB (IEEE802.15.1) (IEEE802.15.13) 2.4 GHz GFSK/FHSS 3.1-10.6 GHz MCOFDM 0 dbm -41.3 dbm/mhz 721 Kbps 10 2 ~10 3 Mbps 7 Slaves /1 Maser pico-ne. PC, Priner Key board Audio ses Hands free ZigBee Alliance Applicaion layer (APL) (User made) Applicaion inerface Nework layer (NWK) Media access conrol layer (MAC) IEEE (Communicaion beween nodes, ec.) 802.15.4 Physical layer (PHY) (Radio regulaions, ec) Figure 2: Proocol srucure for ZigBee. 3. CONVENTIONAL ULTRASONIC MEASURING METHODS One of he images for sensor nework insalled in homes and offices is shown in Fig. 4. Many sensor nodes wih various sensors will be arranged, where nodes can communicae one anoher via ZigBee. Sensed signals from all nodes are gahered o a cener node. The cener node no
PIERS ONLINE, VOL. 5, NO. 4, 2009 323 only supervises sensor nodes and processes colleced daa bu also sends conrol signals o oher insallaions. Ulrasonic devices wihin sensor nodes ransmi and receive ulrasonic waves o measure he disances beween sensor nodes and refleced objecs. Sar-link ype Tree-link ype Mesh-link ype Figure 3: Nework opology for ZigBee. Only sar-link ype is acceped for Blueooh and radio LAN. All hree link ypes are possible for ZigBee. Sensor nodes Sensor node Sensor node Cener node ZigBee Ulrasonic waves Figure 4: Image eample for sensor nework wih ulrasonic posiioning mehod. Two major measuring mehods have been used in convenional posiioning sysems. One is a pulse-echo mehod, and he oher is a code-division mehod [2]. Assuming wo objecs as shown in Fig. 5, he pulse-echo mehod measures ime delays beween he ransmied and received burs-ype ulrasonic pulses as shown in Fig. 6. In his case, he widh of received pulses is spread comparaively compared wih ha of he ransmied pulses, which requires very narrow ransmied pulse o achieve enough space resoluion. However, if we keep he same ransmied energy he ampliude of ransmied pulses mus be increased wih narrowing heir widh. Therefore, high volage handling capabiliy is needed for a final sage amplifier in he ransmier, which reveals ha adoping his mehod o sensor nodes is very difficul. l 1 l1 Objec 1 Transmier l 2 Receiver Ulrasonic waves l 2 Objec 2 Figure 5: Measuremen model wih wo objecs as well as ransmier and receiver. Figure 6: Transmied and received ulrasonic pulses for pulse-echo mehod.
PIERS ONLINE, VOL. 5, NO. 4, 2009 324 The oher code-division mehod uses Binary-phase-shif-keying (BPSK) signals as ransmied ulrasonic waves shown in Fig. 7 s lef figures. The 0/-phase combinaion is deermined based on specific codes, such as Barker, M-sequence, and Gold codes. Oupu signals from a sliding correlaor wihin he receiver have sharp peaks which correspond o auo-correlaion funcion beween he coded signal in received ulrasonic waves and a replica signal, i.e., reverse-order-coded signal, from he receiver. This mehod provides high space resoluion as shown in Fig. 7. However, very high speed digial-signal-processing (DSP) ICs and large memories are necessary o achieve funcion of he sliding correlaor, which also reveals i difficul o adop his mehod o sensor nodes. Figure 7: Transmied and received ulrasonic pulses for code-division mehod. Lef figures show specific code and BPSK signals. 4. NOVEL ULTRASONIC POSITIONING METHOD FOR SENSOR NETWORK ZigBee which uses 2.4 GHz has been regulaed by IEEE802.15.4 as one of radio sandards for low daa-rae communicaions media such as a sensor nework [4]. As a block diagram is shown in Fig. 8, he sensor node used in convenional ZigBee sysem consiss of 2.4-GHz VCO (Volage- Conrolled Oscillaor) locked o TCXO (Temperaure-Compensaed Xal Oscillaor, i.e., 13 MHz) and oher circui componens. We have proposed a new sensor node srucure which is consruced wih no only above circuis bu also new ulrasonic-posiioning devices as shown in Fig. 8. 2.4GHz VCO (2.4GHz) Demod Mod TCXO 2.4GHz Demod VCO (2.4GHz) Mod Programmable 1 couner N TCXO X Componen Y Componen 2 Transmier Mier Mier Receiver Figure 8: Block diagram for ZigBee-based sensor node. Convenional node. New node wih ulrasonicposiioning devices. A same model as shown in Fig. 5 which consiss of an ulrasonic ransmier, an ulrasonic receiver and wo reflecing objecs is considered. In general, an ulrasonic ransducer has frequency characerisics. Assuming ha he ransmied waves from he ransducer have a frequency bandwidh from f 1 o f 2, and have single-peaked characerisics for ampliude and fla characerisics for phase respecively wihin he bandwidh as shown in Fig. 9, he received waves have reducedampliude and increased-phase characerisics due o he propagaion and he reflecion as shown in Fig. 9. A ransmission funcion, G(ω), beween he ransmier and he receiver can be obained by a fracion beween he characerisics in Figs. 9 and. Therefore, he magniude of G(ω), G(ω), is calculaed as he relaive ampliude beween Figs. 9 and. The argumen of G(ω), G(ω), is given by ha in Fig. 9 because he phase of he ransmied waves is assumed o be zero. An Inverse Fourier Transform of G(ω) leads o he impulse response beween he ransmier and he receiver. This impulse response includes signals of sin()/-shaped funcion, as shown in Fig. 10. Cener of he each signal of sin()/-shaped funcion reveals a ime delay of raveling ulrasonic waves beween he ransmier and he receiver way of he corresponding reflecing objec. Thus we can obain he disance from he ransmier/receiver o he objec by muliplying he ime delay and wave velociy, i.e., abou 340 m/s.
PIERS ONLINE, VOL. 5, NO. 4, 2009 325 Phase Ampliude 0 f 1 Frequency f 2 Phase Ampliude 0 f 1 Frequency f 2 Figure 9: Ampliude and phase characerisics of ulrasonic coninuous waves. Acual daa a discree frequencies have values as indicaed by crosses. Transmied waves. Received waves. Figure 10: Impulse response, Inverse Fourier Transform of G(ω), beween ransmier and receiver. In an acual model, he ransmier/receiver devices are included in a sensor node as shown in Fig. 8. We divide he frequency from f 1 o f 2 ino n + 1 of discree frequencies, i.e., f(1) = f 1, f(2) = f 1 + (f 2 f 1 )/n,..., f(n + 1) = f 2. These frequencies are also deermined same as discree frequencies used in IFFT (Inverse Fas Fourier Transform) procedure, and can be produced by couning signal, i.e., 13-MHz signal for eample, from TCXO using a programmable couner as shown in Fig. 8. Arbirary couning numbers, Ns, are designaed from he cener node via ZigBee, which provides signals a several ens KHz o he ransmier. Eamples of ransmied waves a he above n+1 of discree frequencies are shown in Fig. 11, while hose of he received waves are shown in Fig. 11. One ransmier (sensor node) ransmis Fig. 10 s waves, and several receivers (sensor nodes) around he ransmier receive Fig. 10 s waves. In each receiver, only ampliudes and phases of he received waves are measured, i.e., he crosses shown in Fig. 9, and hey are sen o he cener node via ZigBee. Therefore, sensor nodes can achieve very low-power consumpion because hey only ransmi and receive ulrasonic coninuous waves wih small ampliude. In he cener node, IFFT procedure is eecued on he basis of daa for ampliudes and phases from sensor nodes. So, delay imes, i.e., disances, from sensor nodes o objecs are obained as impulse response beween he ransmier and receivers. Tangible advanages of he proposed sysem are ha disance informaion can be auomaically gahered in he cener node, and all digial signal processing procedures such as IFFT are eecued only in he cener node wih anoher power supply. f(1)=f 1 f(n+1)=f 2. f(1)=f 1 f(n+1)=f 2. Figure 11: Coninuous waves a n+1 of discree frequencies from f(1) = f 1 o f(n+1) = f 2. Transmied waves. Received waves. 5. EXPERIMENTAL RESULTS In order o confirm our proposal, we eperimenally invesigaed he mehod using a simple model shown in Fig. 12. The ransmier and he receiver are arranged abou 50 cm apar o each oher.
PIERS ONLINE, VOL. 5, NO. 4, 2009 326 As a comparison, we firs measured he same disance by a convenional pulse-echo mehod wih burs ype of 40-KHz ulrasonic pulses. Eperimenal resuls of he convenional mehod are shown in Figs. 13 and, where and show he ransmied and received pulses, respecively. The received pulse is delayed by abou 1.5 msec which corresponds o abou 50 cm. Transmier (Sensor node) Receiver (Sensor node) Signal generaor 2 CH Digial IFFT using PC oscilloscope (ZigBee) (Cener node) Figure 12: Eperimenal se-up wih ransmier and receiver abou 50 cm apar o each oher. Transmied ulrasonic pulse Received ulrasonic pulse 1.5 msec ( 50 cm) Figure 13: Eperimenal resuls for convenional pulse-echo mehod. Transmied pulse. Received pulse. In he new mehod, he ransmied and received coninuous waves are displayed in an oscilloscope, and measured daa of relaive ampliudes and phases beween hem are sen o a PC as shown in Fig. 12. Relaive ampliudes and phases are shown in Figs. 14 and, respecively. From he figures, 3-dB bandwidh of he ransducer is abou 1.9 KHz, and almos no waves can be ransmied a he ouside frequency range of 37.4 43.5 KHz. Impulse response characerisics beween he ransmier and he receiver obained by IFFT procedure on he basis of daa in Figs. 14 and are shown in Fig. 15. The disance of abou 50 cm can be clearly recognized, and he hreshold characerisics are beer han hose obained by he convenional mehod. These resuls confirmed validiy of our proposed novel mehod. 200 Ampliude 3dB Bandwidh Phase (deg.) 100 0 35 36.25 37.5 38.75 40 41.25 42.5 43.75 45-100 35 36.25 37.5 38.75 40 41.25 42.5 43.75 45 Frequency (KHz) -200 Frequency (KHz) Figure 14: Measured daa for proposed mehod. Ampliude characerisics. Phase characerisics. IFFT Ampliude 0 10 20 30 40 50 60 70 80 90 Disance (cm) Figure 15: Measured disance wih proposed mehod, i.e., IFFT resuls using Fig. 14 s daa.
PIERS ONLINE, VOL. 5, NO. 4, 2009 327 6. CONCLUSIONS Sensor nework which consiss of small-sized radio-communicaion infrasrucures has been invesigaed as mos promising means o monior and conrol home/office circumsances. We proposed a novel ulrasonic disance measuring mehod which can be used as ulrasonic posiioning insalled in sensor nework. We also devised a new sensor node srucure which included no only nework funcions bu also ulrasonic sensing devices. The fundamenal eperimens wih he ransmier and he receiver facing o each oher showed validiy of he proposed mehod as well as possibiliy of new nework sysems including he posiioning mehod. REFERENCES 1. Home Page of Kogakuin Universiy (hp://www.ns.kogakuin.ac.jp/ wwa1022/). 2. Dion, R. C., Spread Specrum Sysems, John Wiley & Sons, 1976. 3. Japanese paen pending. 4. IEEE Sandard 802.15.4: Wireless Medium Access Conrol (MAC) and Physical Layer (PHY) Specificaions for Low Rae Wireless Personal Area Neworks (LR-WPANs), 2003.