Development of FM-CW Radar System for Detecting Closed Multiple Targets and Its Application in Actual Scenes

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1 XX by the authors; liensee RonPub, Lübek, Germany. This artile is an open aess artile distributed under the terms and onditions of the Creative Commons Attribution liense ( Open Aess Open Journal of Internet of Things (OJIOT) Volume X, Issue X, XX ISSN Development of FM-CW Radar System for Deteting Closed Multiple Targets and Its Appliation in Atual Senes Kazuhiro Yamaguhi A, Mitumasa Saito B, Takuya Akiyama A, Tomohiro Kobayashi A, Naoki Ginoza A, Hideaki Matsue A A Tokyo University of Siene, Suwa, 5-1 Toyohira, Chino, Nagano, Japan, yamaguhi@rs.tus.a.jp, matsue@rs.suwa.tus.a.jp B CQ-S net In., Torigoe 7-8, Kanagawa-ku, Yokohama-shi, Kanagawa, Japan, 1-64, info@q-snet.om ABSTRACT In this paper, detetion method for 4 GHz band FM-CW radar system under losed multiple targets with small displaements environment was proposed, and its performanes were analyzed by using omputer simulation. The proposed detetion method used a differential detetion method for removing any signals from bakground objets, and also used a tunable FIR filtering in signal proessing for deteting multiple targets. The proposed detetion method enabled to detet both the distane and small displaement at the same time for eah target orretly from the reeived signal inluding all of signals from the targets at the FM-CW radar. The basi performanes for FM-CW radar were analyzed in omputer simulation, and field experiments for deteting target under atual environments. The results showed that the proposed differential detetion ould only measure the desired targets, and the human breathing ould also be deteted in a hospital sene. Furthermore, under losed multiple targets environments, we showed the problems for deteting both distane and small displaements of multiple targets at the same time by using a single radar. Computer simulations were arried out for evaluating the proposed detetion method with the tunable FIR filtering for FM-CW radar and analyzing the performane aording to the parameters under losed multiple targets environment. The results in omputer simulation showed that the proposed detetion method ould detet both the distane and small displaement orretly under losed multiple targets environment. TYPE OF PAPER AND KEYWORDS Regular researh paper: FM-CW radar, distane measuring, small displaement measuring, multiple targets detetion, tunable FIR filtering 1 INTRODUCTION Reently, rapidly evolving wireless ommuniation tehnologies provides us to ommuniate various information from a lot of manufatures in widely tehnologies field. IoT (Internet of Things) is popularly known as a key topi for developing system and servies, and it enables various physial devies to ollet various things suh as sensor information. As one of sensing appliations, radar has been employed to detet in widely areas suh as on the ground, on the sea, in the air, in spae. The radar systems an detet various information aording to appliation areas by transmitted and reeived through radio wave. Radar systems with 4 GHz band is based on ARIB 1

2 Open Journal of Internet of Things (OJIOT), Volume X, Issue X, XX Signal D/A VCO BPF! Tx & ' Target 1 FFT Display Signal proessing A/D BPF Rx & ( Target Target #$% " & ) & distane from the radar Figure 1: Blok diagram of a FM-CW radar system standard T73 [1] in Japan as sensors for deteting or measuring mobile objets for speified low power radio station. And the 4 GHz band radar system ould be applied in various field suh as seurity, medial imaging and so on under indoor and outdoor environments. Various radar systems were reported [, 3, 4, 5]. Pulsed radar systems an measure the period between the transmitted and reeived signals. The pulsed radar an detet the distane in far field; however, the target in near field an not be deteted orretly. Doppler radar systems an measure the frequeny differene between the refleted and transmitted signals. The Doppler radar an detet the moving veloity of the target; however, the distane of the target an not be deteted. FM-CW (Frequeny- Modulated Continuous-Wave) radar systems [6, 7] is the most widely used for deteting the distane of the target objet in near field and the small displaement of the target. As previous study, we reported the design, performane analysis, and appliations with 4 GHz band radar system for deteting both the distane from the radar and the small displaement for human breathing [8]. The radar system ould detet both the distane to the human from the radar and the small displaement of the human breathing orretly; however, it was diffiult for deteting the distanes and displaements for multiple humans at the same time. In order to detet the distanes and displaements under losed multiple targets environment, we proposed a detetion method for signal proessing with a tunable FIR filter in the FM-CW radar system [9]. Furthermore, performane analysis for FM- CW radar system was shown in omputer simulations. In this paper, the proposed detetion method onsidering both the differential detetion and the tunable FIR filtering for deteting both the distanes and small displaements under single and losed multiple targets environment. Moreover, appliations based on IoT for deteting the human movements in atual senes were desribed. This paper onsists of the following setions. In Setion II, we desribe the priniple of a FM-CW radar system and its basi performane under single target environment. In Setion III, we desribe the proposed detetion method under single target environment. In Setion IV, we desribe the proposed detetion method under multiple targets environment. In Setion V, we disuss the results of omputer simulation and field experiments. Finally, Setion VI onludes this paper. FM-CW RADAR SYSTEM.1 Priniple of FM-CW radar Figure 1 shows the blok diagram of a FM-CW radar system [1]. FM-CW (Frequeny-Modulated Continuous-Wave) radar was one type of radar whih was transmitting a ontinuous arrier modulated by a periodi funtion suh as a sawtooth wave to provide range data shown in Figure. In the FM-CW radar system, frequeny modulated signal at the VCO is transmitted from the transmitter Tx; then, signals refleted from the targets are reeived at the reeiver Rx. Transmitted and reeived signals are multiplied by a mixer, and beat signals are generated as multiplying the two signals. The beat signal pass through a low pass filter; then, an output signal is obtained. In this proess, the frequeny of the input signal is varied with time at the VCO. The modulation waveform with a linear sawtooth pattern [11] as shown in Figure. This figure illustrates frequeny-time relation in the FM-CW radar, and the red line denotes the transmitted signal and the blue line denotes the reeived signal. Here, f denotes the enter frequeny, f w denotes the frequeny bandwidth for sweep, and t w denotes the period for sweep. We define that the transmitting signal V T (f, x) is represented as V T (f, x) = Ae j πf x, (1) where f denotes a frequeny at a time, x denotes a distane between a target and the transmitter, A denotes an amplitude value, and denotes the speed of light.

3 Frequeny Kazuhiro Yamaguhi, Mitumasa Saito, Takuya Akiyama, Tomohiro Kobayashi, Naoki Ginoza, Hideaki Matsue: Development of FM-CW Radar System for Deteting Closed Multiple Targets and Its Appliation in Atual Senes By using signal proessing, a distane and a displaement for the target are given from the generated output signal in Equation (4). By using the Fourier transform, the distane spetrum of the output signal P (x) is alulated as follow. " # + "! % " # $ "! %! " Transmitted signal! Time " # : enter frequeny!: bandwidth of sweep frequeny!: sweep time Reeived signal Figure : Sawtooth frequeny modulation The refleted signal V R (f, x) is represented as V R (f, x) = K Aα k γ k e jφ k e j πf (d k x), () where γ k and φ k are the refletive oeffiients for amplitude and phase on kth target, respetively. α k denotes an amplitude oeffiient for transmission loss from the kth target, and d k is the distane between the transmitter and the kth target. Here, at the reeiver whose position is x =, Equation () is rewritten as V R (f, ) = K Aα k γ k e jφ k e j πf (d k). (3) The beat signal is generated as multiplying the transmitted signal in Equation (1) and the reeived signal in Equation (3) at the position x =. After through LPF, the output signal V out (f, ) is generated by V out (f, ) = K A α k γ k e jφ k e j 4πfd k. (4) # P (x) = = f + f w f fw f+ f w f f w V out e K K = A α k γ k e jφ k 4πf j df A α k γ k e jφ k e j 4πfd k e f+ f w f f w [ K = A α k γ k e jφ k e j 4πf (d k x) 4πfx j e j 4πf(d k x) df df { } ] πfw (d k x) f w sin. (5) In this equation, the funtion of sin (x) denotes sin (x) = sin x x. (6) The amplitude value of the distane spetrum P (x) in equation (5) is given as P (x) = A K α k γ k e jφ k e j 4πf (d k x) { } πfw (d k x) f w sin [ A f w K α k γ k { } ] sin πfw (d k x), (7) and we have equality if and only if the phase omponents ϕ k + 4πf (d k x) about all of k are equal. Here, we assumed that the number of target is 1. The distane spetrum in equation (5) is rewritten as [ P (x) = A α 1 γ 1 e jφ 1 e j 4πf (d 1 x) { } ] πfw (d 1 x) f w sin, (8) and the amplitude value of distane spetrum is given as { } P (x) = A πfw (d 1 x) α 1 γ 1 f w sin. (9) This equation indiates that the distane for the target is generated by the amplitude value of distane spetrum. 3

4 !! Open Journal of Internet of Things (OJIOT), Volume X, Issue X, XX Table 1: Parameters in omputer simulations Parameters Values Center frequeny f 4.15 (GHz) Bandwidth of sweep frequeny f w 5, 1,, 4 (MHz) Sweep time t w 14 (µs) Sampling time for sweep.1, 1, 1 (µs) Number of FFT points 496 Window funtion hamming Sampling time for sweep = 1! 5 MHz 1 MHz MHz 4 MHz The phase value of distane spetrum P (x) is represented as P (x) = φ 1 + 4πf (d 1 x) = θ 1 (x). (1) Here, θ 1 (x) satisfy π θ 1 (x) π, then the displaement for the target is ( π φ 1) 4πf d 1 (π φ 1) 4πf. (11) If the phase value satisfies ϕ 1 =, equation (11) is rewritten as 3.11 [mm] d [mm] with f = 4.15 [GHz]. That is, the small displaement of the target within ±3.11 [mm] is generated by the phase value of distane spetrum. On the other hands, the maximum distane for measuring d max is f w f = [Hz], t w /t s d max = [m], (1) 4 f where t w denotes the sweep time, t s denotes the interval time for sampling. For example, in the ase with t w = 14 µs and t s = 1 µs, the maximum distane is d max = 384 [m].. Analysis of Basi Performanes At first, we desribes the basi performane about the FM-CW radar with 4 GHz band. Parameters for omputer simulation are listed in table 1, and the parameters were determined as ARIB standard T73[1]. Center frequeny was 4.15 GHz, bandwidth are 5, 1,, and 4 MHz. Note that the 4 MHz bandwidth was only used for the omputer simulation beause of standards in the Radio Law in Japan. Sweep time was 14 µs, sampling times for sweep were.1, 1, 1 µs, number of FFT points was 496, and the hamming windows was adapted as the window funtion in signal proessing. We assumed that a stati target is loated at 1 m from the transmitter and reeiver, and the distane spetrums Measured distane [m] Figure 3: Resolution for distane spetrum aording to bandwidth of sweep frequeny f w..1"#,1"# " # = MHz 1"# Measured distane [m] Figure 4: Error value for distane spetrum aording to sampling time for sweep. are outputted with various parameters. Figure 3 shows the amplitude value for distane spetrum versus measured distane with various sweep bandwidth. The result shows that the sweep bandwidth influened the distane resolutions and widely bandwidth ould improve the resolution. In the ase with t s = 1 µs, the distane resolutions with f w = 5, 1,, 4 MHz were ±5, ±1.5, ±1, ±.5 m, respetively. Figure 4 shows the amplitude value for distane spetrum versus measured distane with various sampling time. The result shows that the sampling interval influened the error about the measured distane and shortly sampling interval ould redue the error value for distane. In the ase with f w = MHz, the error values about the measured distane with t s = 1 µs was about.5 m. Figure 5 shows the result for measuring a slowly moving target with f w = MHz and t s = 1 µs. The target moved from 1 m to m at intervals of.5 m on eah time step. Figure 5(a) shows the amplitude value versus measured distane versus target distane with 3- dimensional viewing, and Figure 5(b) shows measured distane versus target distane with -dimensional view- 4

5 Kazuhiro Yamaguhi, Mitumasa Saito, Takuya Akiyama, Tomohiro Kobayashi, Naoki Ginoza, Hideaki Matsue: Development of FM-CW Radar System for Deteting Closed Multiple Targets and Its Appliation in Atual Senes! Measured distane [m] All of spetrums: Measured distane Spetrums of the other objets:! Spetrum of the target objet! = MHz, Sampling time for sweep = 1! Target distane Target distane [m] (a): 3D view. (a): without differential detetion. Measured distane Measured distane [m] "# = MHz Sampling time for sweep = 1! Target distane Spetrum of the target objet! = MHz, Sampling time for sweep = 1! Target distane Target distane [m] (b): D view. Measured displaement [mm] (b): with differential detetion (Proposed). Figure 5: Distane spetrum for measuring moving Figure 7: Distane spetrum for measuring moving target. target distane with / without the differential detetion under the environments whih multiple objets are loated.! = MHz Sampling time for sweep = 1! ment and it is not orresponding to the absolute distane between the reeiver and the target objet. The small displaement within ± 3.11 mm was orretly measured with the parameters of the FM-CW radar system in this paper although the displaement more than ±3.11 mm had unertainty. Target displaement [mm] 3 P ROPOSED T ECHNIQUES FOR SINGLE TAR GET DETECTION Figure 6: Measured displaement. 3.1 ing. The olor in (b) is orresponding to the strength of the amplitude value in (a). From these figures, it was onfirmed that the distane ould be measured orretly aording to the positions of the moving target. Figure 6 shows the result for measuring a target with small displaement, and the measured displaement versus target displaement is outputted. The objet was loated at 1 m from the reeiver, and the objet moved from -5 mm to 5 mm at intervals of.1 mm. The small displaement ould be measured by the phase value of distane spetrum, and the measured displaement was orresponding to the target displaement. Note that the measured displaement denotes the relative displae- Detetion for single target As mentioned in the above setion, the FM-CW radar system ould measure the distane and the small displaement for single target at the same time. However, it was a speial ase that only the refleted signal on a target ould be reeived at the reeiver. In general, the reeiver may reeive the refleted signals from many objets. Therefore, when there was some objets for measuring the target distane, signal proessing for deteting the distane spetrum from the only target would be required. The proposed method removes the signals from the other objets by using the differential detetion of distane spetrum. Figure 7 shows the distane spetrum 5

6 Open Journal of Internet of Things (OJIOT), Volume X, Issue X, XX Table : Parameters in filed experiments FM-CW radar Parameters Center frequeny f Bandwidth of sweep frequeny fw Sweep time tw Sampling time for sweep ts Outputting power on Transmitting Antenna gain Range of distane Range of relative displaement Distane Small displaement Figure 8: An setting example of FM-CW Radar for deteting human breathing 7 (mw) 11 (dbi) 1 (m) ±3.11 (mm) Time [s] Measured distane [m] (a): without differential detetion. Time [s] (b): with differential detetion (Proposed). Figure 9: Distane spetrum for measuring moving target distane with / without the differential detetion. 3. Field Experiments and Appliation (µs) 1 (µs) Measured distane [m] when the target objet moves from 1 m to m and the other objets are loated at 15 m and m. The transmitted signal is refleted on the target and the other objets, the reeiver reeives several refleted signals. Therefore, the distane spetrum of the other objets are also generated by the FM-CW radar system in Figure 7(a), and the distane spetrum of the target an not be deteted learly. In partiular, when the refletion oeffiient of the target is lower than that of the other objets, the distane spetrum of the other objet has higher amplitude value than that of the target. In the proposed differential detetion, at first, the distane spetrum of the other objets P is generated beforehand in Figure 7(a). Then, the distane spetrum of the target and the other objet P is subtrated by P. By using the differential detetion, distane spetrum removed the distane spetrum of the other targets is generated as P P. Therefore, the distane spetrum of the desired target is only deteted. Figure 7(b) shows the distane spetrum by using the proposed differential detetion method, and the distane spetrum of the target is orretly measured. As ompared with the measured distane spetrums in Figure 7(a) and (b), it is learly onfirmed that the proposed method an detet target distane by using the differene detetion. The proposed differential detetion an effetively detet the moving or stati target distane from multiple refletions of the bakground stati objets. Values 4.15 (GHz) (MHz) Setup ondition for field experiments In order to evaluate the effetiveness of the proposed method for deteting the target distane and displaement, we developed a FM-CW radar system and arried out the experiments with the radar system in atual environment. Table lists the parameters, and the developed FM-CW radar system got a ertifiate of onformity with tehnial regulations in Artile 38-6 Paragraph 1 of the Radio Law in Japan, and developed FM-CW radar system was aommodate to ARIB standard T73 in Japan [1]. 3.. Results in field experiments Figure 9 shows the distane spetrum of a moving target. A person walked away from the FM-CW radar and then ame lose between m to 1 m. In Figure 9(a), several distane spetrums of the person and the bakground objets were outputted. The distane spetrum of the moving person was not learly deteted in Figure 9(a) beause of the refleted signals from bakground objets. In order to detet the distane spetrum of the moving 6

7 Measured small displaement [mm] Kazuhiro Yamaguhi, Mitumasa Saito, Takuya Akiyama, Tomohiro Kobayashi, Naoki Ginoza, Hideaki Matsue: Development of FM-CW Radar System for Deteting Closed Multiple Targets and Its Appliation in Atual Senes Time [s] 5 seonds Figure 1: Displaement for measuring the movement of human breathing. Measured distane [m] 1. Without any person. Refletion on the human body Time Measured small displaement [mm] 3. Breathing detetion (a) (b) Alert information Types of status Figure 11: Example of appliation. Time Status for individual targets person with the differential detetion method, the distane spetrum without the person was measured beforehand. By generating the distane spetrum of the bakground objets beforehand, the distane spetrum of the moving person was orretly deteted in Figure 9(b) with the proposed differential detetion. Therefore, the FM- CW radar system ould measure movement of the target person effetively. Figure 1 shows the result of measuring the small displaement for human breathing. The human s hest movement was measured within the range of relative small displaement. In Figure 1, it was deteted that the period of breathing was about 4 s and the breathing movement was about within ± mm Example of Appliation In this setion, we show an example of appliation with 4 GHz FM-CW radar system. Figure 8 shows a setup of the FM-CW radar system for deteting human breathing in atual senes. The FM-CW radar satisfied the safety guideline, and the details of the safety guideline is desribed in Appendix. Figure 11(a) shows the example of the results for deteting human breathing of single target in a room of a hospital. The distane spetrum in this example was measured as following flow. 1. Measuring distane spetrum without any person.. A person omes to the bed. The radar reeived signals from human s body. 3. The person lies asleep on the bed. The radar detets the person s breathing movement. By generating the distane spetrum of the bakground objets without the person, the distane spetrum of the person was only deteted. When the person omes within the range of radar, the radar system ould detet refleted signals from the person, and the distane spetrums of the human s body were deteted. After the person lied down on the bed, the radar system ould detet the small displaement for the person s breathing movement. By using the differential detetion method, the distane and small displaement of the moving objet were learly deteted. As onneting the developed FM-CW radars in several rooms in the hospital, deteting several targets ould be realized. An example of monitoring several targets is shown in Figure 11(b). The developed FM-CW radars were onneted the network system, and the information of deteting the distane and small displaement were sent to server in nurse station. In the nurse station, status of several targets ould be monitored, and the alert information suh as falling off the bed and stopping the human breathing ould be monitored. 4 PROPOSED TECHNIQUES FOR MULTIPLE TARGETS DETECTION 4.1 Problems for multiple targets detetion As mentioned in the above setion, the FM-CW radar system ould detet both the distane and displaement orretly under single target environments; however, the FM-CW radar ould not detet both the distane and displaement orretly under losed multiple targets environments. In order to realize detetion for losed multiple targets, we propose the detetion method by using the signal proessing with a tunable FIR filter. 7

8 Power Small displaement Open Journal of Internet of Things (OJIOT), Volume X, Issue X, XX Ceiling FM-CW radar Distane:.m Distane: 1.m Small displaement Small displaement Signal after A/D proess Signal proessing FFT For target 1 1. Peak position detetion. Tunable bandpath FIR filter Display amplitude value Display phase value.5mm.mm For target Time 1.s Target 1 Target 7.5s Figure 1: Setup onditions with targets Only target 1 Only target target 1 + target Distane 7.5s 1.s Time.5mm.mm Figure 13: Simulated results of detetion for losed multiple targets 4. FIR filtering The proedures of the proposed detetion method for multiple losed targets is as follow. We assumed that the FM-CW radar is loated a short distane from a bed as shown in Figure??. In this situation, the radio waves were radiated from the FM-CW radar, and targets lied down on the bed. The distanes from the radar to eah target were different, so that the peaks of distane spetrum were deteted at different frequeny. In this ase, the deteted result shown in Figure 13 is sum of these targets, and it is diffiult for deteting both the distane and phase values for eah user orretly. In order to solve this problem, signal proessing with the tunable FIR filter was used in the proposed detetion method. Figure 14 shows the blok diagram of the proposed detetion method. At first, the A/D onverted signal is arried out the FFT operation, and the distane 1. Peak position detetion Amplitude [A.U.] Beat frequeny [khz]. Tunable band-path FIR filter Amplitude [A.U.] Beat frequeny [khz] Figure 14: Blok diagram of the proposed multiple targets detetion in signal proessing Table 3: Parameters in omputer simulations 1,, 4, 8 Parameters Values Center frequeny f 4.15 (GHz) Bandwidth of sweep frequeny f w (MHz) Sweep time t w 56, 51, 14, 48 (µs) Bandwidth for FIR filter B, 4, 8, 16, 3 (Hz) Number of FFT points 496 Window funtion hamming spetrum is obtained. After proessing the FFT operation, the peaks of amplitude value of the distane spetrum are alulated for eah user. In the peak position detetion proessing, the two frequeny value aording to the targets is obtained; then, FIR filters are designed aording to the peak positions of desired targets. The tunable FIR filter has the enter frequeny orresponding to the alulated frequeny in the peak position detetion, and the linear property for the phase value. By using the designed FIR filter, band-path filtering operation is arried out for the distane spetrum. After through band-path filter, the amplitude and phase value for eah target are deteted orretly. 4.3 Computer Simulations Setup ondition In order to evaluate the performane for FM-CW radar system with the proposed method under multiple targets environment, we arried out omputer simulations. Parameters for omputer simulations are listed in Table 3, and the parameters are also based on ARIB standard T73 8

9 Small displaement [mm] Amplitude [A.U.] Kazuhiro Yamaguhi, Mitumasa Saito, Takuya Akiyama, Tomohiro Kobayashi, Naoki Ginoza, Hideaki Matsue: Development of FM-CW Radar System for Deteting Closed Multiple Targets and Its Appliation in Atual Senes Table 4: Setup onditions for targets Parameters Target 1 Target Distane 1. (m). (m) Amplitude of Displaement.5 (mm). (mm) Period of displaement 1. (s) 7.5 (s) [1]. Center frequeny was 4.15 GHz, and frequeny bandwidths were 1,, 4, and 8 MHz. Note that the 4 and 8 MHz bandwidth were only used for the omputer simulation beause of standards in the Radio Law in Japan. Sweep times were 56, 51, 14, and 48 µs, sampling time of sweep was.1 µs, number of FFT points was 496, and the hamming windows was adapted as the window funtion in signal proessing. The bandwidths for FIR filter were, 4, 8, 16, and 3 Hz. In the following setions, we desribe the evaluation values for analyzing the results of multiple targets detetion, and the performane analysis aording to bandwidth for sweep frequeny, sweep time, bandwidth for FIR filter, and position of target are desribed Evaluation values for amplitude and phase values Figure 15 shows the evaluation values for deteting the amplitude and phase values of the distane spetrum of multiple targets. As evaluation values, we defined the degree of amplitude separation for amplitude value and NMSE for phase value. The degree of amplitude separation is represented by S k = 1 log P min P k = 1 log P (f min) P (f k ) [db], (13) where k denotes the number of target, S k denotes the degree of amplitude separation, P min denotes minimal value of amplitude whose frequeny is f min, and P k denotes the peak value for k-th target with frequeny of f k. The NMSE for phase value is represented by NMSE = N d i d i i=1 d i, (14) where N denotes the number of sampling points, d i and d i denote the sampled signals of deteted and setuped values for a target, respetively Performane for Bandwidth of sweep frequeny Figure 16 shows the evaluation values versus the bandwidth of sweep frequeny f w for amplitude value in (a) Minimal value!"# = $!"# Maximal value! = "! Maximal value! = "! 1! "#$ 3 % 4 5 Beat frequeny [khz] Setuped value! (a): Amplitude Deteted value Setuped value Deteted value! " Time [s] (b): Phase Figure 15: Definitions of evaluation values for omputer simulation and phase value in (b). As shown in (a), the degrees of amplitude separation were about -.5 db and -19 db with f w = 1 MHz and f w = 8 MHz, respetively. Beause the resolution of the distane spetrum was inreased as an inreasing the bandwidth of sweep frequeny, the separation of targets for amplitude value beome easily. As shown in (b), NMSE was about % with the bandwidth of sweep frequeny f w = 1 MHz, and NMSE was also improved as an inreasing the bandwidth of sweep frequeny. Although there was a few disadvantage for NMSE of target, the multiple targets detetions ould orretly ahieved beause the degree of amplitude separation with -1 db and NMSE with 6 % were enough 9

10 NMSE NMSE Degree of amplitude separation [db] Degree of amplitude separation [db] Open Journal of Internet of Things (OJIOT), Volume X, Issue X, XX - -4! = 14 "# $ = Hz Target 1 Target Target 1 Target " # = MHz = Hz !: Bandwidth of sweep frewueny [MHz] !: Sweep time [us] (a): Amplitude (a): Amplitude 7.% 6.%! = 14 "# $ = Hz 7.% 6.% 5.% 5.%! = MHz = Hz 4.% 4.% 3.%.% Target 1 Target 3.%.% Target 1 Target 1.% 1.%.% !: Bandwidth of sweep frequeny [MHz].% !: Sweep time [us] (b): Phase (b): Phase Figure 16: Evaluation values versus bandwidth of sweep frequeny values for deteting multiple targets in pratial use Performane for Sweep time Figure 17 shows the evaluation values versus the sweep time t w for amplitude value in (a) and phase value in (b). As shown in (a), the degree of amplitude separation for target 1 kept about -4 db in aordane not to the sweep time. The degree of separation for target had -1 db during the sweep time t w = µs. In the ase with t w = 14µs, the degree of amplitude separation was almost db. That is, it was diffiult to detet the peak value of amplitude for target. Moreover, ompared to the result in (b), the worst NMSE for Figure 17: Evaluation values versus sweep time target was about 4 % with t w = 48 µs. Beause the resolution for distane spetrum was dereased as an inreasing the sweep time, the sweep time should be less than 14 µs Performane for Bandwidth of FIR filter Figure 18 shows the evaluation values versus the bandwidth of FIR filter B for amplitude value in (a) and phase value in (b). As shown in (a), the degree of amplitude separation for target 1 kept - db in aordane not to the bandwidth of FIR filter B. When B was more than 16 Hz, the degree was more than -1 db, therefore, it was diffiult to detet the peak value. As shown in (b), NMSE for target 1 was less than 3 1

11 NMSE Degree of amplitude seperation [db] Kazuhiro Yamaguhi, Mitumasa Saito, Takuya Akiyama, Tomohiro Kobayashi, Naoki Ginoza, Hideaki Matsue: Development of FM-CW Radar System for Deteting Closed Multiple Targets and Its Appliation in Atual Senes Target 1 Target! = MHz! = 56 "# $: Bnadwidth of FIR filter [Hz] Degree of amplitude seperation [db] ! = 56 "# $ = Hz 5 Target 1 (! = MHz) 6 Target (! = MHz) 3 Target 1 (! =4 MHz) 4 Target (! =4 MHz) 1 Target 1 (! =8 MHz) Target (! =8 MHz) Position of target [m] (a): Amplitude (a): Amplitude 7.% 6.% $! = MHz! = 56 "# 7.% 6.%! = 56 "# $ = Hz 5.% Target 1 5.% 4.% 3.%.% 1.%.% Target $: Bandwidth of FIR filter [Hz] NMSE 4.% 3.%.% 1.%.% Target 1 (! = MHz) Target (! = MHz) Target 1 (! =4 MHz) Target (! =4 MHz) Target 1 (! =8 MHz) Target (! =8 MHz) Position of target [m] (b): Phase (b): Phase Figure 18: Evaluation values versus bandwidth of FIR filter Figure 19: Evaluation values versus positions of target %, but NMSE for target was more than 5 % with B = 16 and 3 Hz. Beause the widely bandwidth of FIR filter was enough not to ut the signal of the other target ompletely, the bandwidth of FIR filter should be less than 16 Hz Performane for distane between targets Finally, we show the result for deteting multiple targets when the target omes lose to the target 1 from m to 1.5 m. Figure 19 shows the evaluation values versus the position of target from the radar for amplitude value in (a) and phase value in (b). The position of the target 1 was 1 m from the radar. Compared to the results, the degree of amplitude separation and NMSE beome depleted as the target approahes to the target 1. As shown in (a), when the bandwidth of sweep frequeny was more than 4 MHz, the degree of amplitude separation had good property whih enough to detet the peaks. However, in the ase with f w = MHz, the degree for target was about -.3 db, and it was diffiult to detet the peaks. As shown in (b), when f w was less than 4 MHz, NMSE ould be kept about less than 5 %. However, in the ase with f w = 8 MHz, NMSE beome depleted. It was diffiult to detet peaks of amplitude for targets as dereasing distane between targets. Therefore, the enter frequeny of FIR filter was not enough to ut the 11

12 Open Journal of Internet of Things (OJIOT), Volume X, Issue X, XX other target s signal, and the imperfet FIR filter influened NMSE values. Although there were a few diffiulty for determining the parameters of the proposed deteting method for FM-CW radar, the proposed deteting method ould be effetive for deteting the distane and the small displaement at the same time under multiple targets environments. ACKNOWLEDGEMENTS A part of this work was supported by Ashita wo Ninau Kanagawa Venture Projet of Kanagawa in Japan. The authors appreiate Prof. Toshio Nojima at Hokkaido University in Japan getting the valuable advies for analyzing the safety properties of the developed FM-CW radar system aording to the safety guideline. 5 DISCUSSION As related works, MIT group reported the radar system for deteting human breathing in [1]. The system ould also detet the movement, and the human breathing in the room ould be deteted learly. However, in Japan, the bandwidth for sweep frequeny was strongly smaller than the MIT s radar system beause of the ARIB standard T73. As shown in figure 3, the resolution was depending on the bandwidth; therefore, the smaller bandwidth influene the deteted distane and small displaement. Moreover, under losed multiple targets environment, some distane between radars and eah target must be required for separating the distane spetrum of eah target. Therefore, in this paper, we used a tunable FIR filtering method in signal proessing for deteting losed multiple targets at the same time. 6 CONCLUSION In this paper, a FM-CW radar system with 4 GHz band with tunable FIR filter for deteting losed multiple moving targets with small displaements was desribed. The proposed deteting method generates tunable FIR filter whose enter frequeny is orresponding to the peak positions of distane spetrum of eah target. The tunable FIR filtered signal an be deteted the distane and displaement for eah target orretly. In omputer simulations, performanes of FM-CW radar system under losed multiple moving targets environment was analyzed in aordane with the bandwidth of sweep frequeny, sweep time, bandwidth of FIR filter, and the distane between targets. As the result, the 4 GHz FM- CW radar with the proposed detetion method ould effetively detet both the distane and the small displaement for eah target under the multiple moving targets environments. And it was onfirmed that the proposed detetion method an detet both the distane and small displaement orretly when the distane between targets was.5 m. As future works, we try to hardware implementation of the proposed FIR filtering and the field experiments. REFERENCES [1] ARIB STD-T73 Rev. 1.1, Sensors for Deteting or Measuring Mobile Objets for Speified Low Power Radio Station, Assoiation of Radio Industries and Businesses Std. [] S. MIYAKE and Y. MAKINO, Appliation of millimeter-wave heating to materials proessing, IEICE transations on eletronis, vol. 86, no. 1, pp , de 3. [3] M. Skolnik, Introdution to Radar Systems. M- Graw Hill, 3. [4] S. Fujimori, T. Uebo, and T. Iritani, Short-range high-resolution radar utilizing standing wave for measuring of distane and veloity of a moving target, ELECTRONICS AND COMMUNICATIONS IN JAPAN PART I-COMMUNICATIONS, vol. 89, no. 5, pp. 5 6, 6. [5] T. Uebo, Y. Okubo, and T. Iritani, Standing wave radar apable of measuring distanes down to zero meters, IEICE TRANSACTIONS ON COMMUNI- CATIONS, vol. 88, no. 6, pp , jun 5. [6] T. SAITO, T. NINOMIYA, O. ISAJI, T. WATAN- ABE, H. SUZUKI, and N. OKUBO, Automotive fm-w radar with heterodyne reeiver, IEICE transations on ommuniations, vol. 79, no. 1, pp , de [7] W. Butler, P. Poitevin, and J. Bjomholt, Benefits of wide area intrusion detetion systems using fmw radar, in Seurity Tehnology, 7 41st Annual IEEE International Carnahan Conferene on, Ot 7, pp [8] K. Yamaguhi, M. Saito, K. Miyasaka, and H. Matsue, Design and performane of a 4 ghz band fm-w radar system and its appliation, in Wireless and Mobile, 14 IEEE Asia Paifi Conferene on, Aug 14, pp [9] K. Yamaguhi, M. Saito, T. Akiyama, T. Kobayashi, and H. Matsue, A 4 ghz band fm-w radar system for deteting losed multiple targets with small displaement, in Ubiquitous and Future Networks (ICUFN), 15 Seventh 1

13 Kazuhiro Yamaguhi, Mitumasa Saito, Takuya Akiyama, Tomohiro Kobayashi, Naoki Ginoza, Hideaki Matsue: Development of FM-CW Radar System for Deteting Closed Multiple Targets and Its Appliation in Atual Senes International Conferene on, July 15, pp [1] M. Skolnik, Radar Handbook, Third Edition. MGraw-Hill Eduation, 8. [11] W. Sediono and A. Lestari, d image reonstrution of radar indera, in Mehatronis (ICOM), 11 4th International Conferene On, May 11, pp [1] F. Adib, H. Mao, Z. Kabela, D. Katabi, and R. C. Miller, Smart homes that monitor breathing and heart rate, in Proeedings of the 33rd Annual ACM Conferene on Human Fators in Computing Systems, ser. CHI 15. New York, NY, USA: ACM, 15, pp [Online]. Available: [13] C95.1-5, IEEE Standard for Safety Levels with Respet to Human Exposure to Radio Frequeny Eletromagneti Fields, 3 khz to 3 GHz, IEEE Std. [14] ICNIRP, ICNIRP STATEMENT on the guidelines for limiting exposure to time varying eletri, magneti, and eletromagneti fields (up to 3 ghz), Health Physis, vol. 97, no. 3, pp , 9. [15] Ministry of Internal Affairs and Communiations dwn/guide38.pdf. APPENDIX In general, eletromagneti wave must be satisfied the guidelines on human exposure to eletromagneti fields, where it have been instituted in various organizations. IEEE C95.1 in USA [13] and ICNIRP in Europe [14] are the guidelines, and MIC also have instituted the guideline in Japan [15]. Developed 4 GHz FM-CW radar in this paper have the properties as follow. The power of the transmitter is 7 [mw], the transmitting antenna gain is 11 [dbi], the effetive radiated power is 88 [mw], the radiation angle of the transmitting wave is about 5 [degree], and the distane between the transmitter and the human is.5 [m]. Aording to the radar equation, the eletri field strength E and the power density P on the human body is alulated as Aording to the guideline [15], these parameters must be satisfied as E 61.4 [V/m], P 1 [mw/m ]. Therefore, the developed 4 GHz FM-CW radar system in this paper suffiiently satisfies the onditions in the guideline. AUTHOR BIOGRAPHIES holography. Kazuhiro Yamaguhi was reeived the M.S. and Ph.D degrees in information siene from Hokkaido University, Hokkaido, Japan, in 9 and 1. He is urrently an Assistant Professor at the Tokyo University of Siene, Suwa, in Japan. His researh interests inlude Internet of Things, wireless ommuniation, signal and image proessing, and Mitsumasa Saito was reeived the B.S. degree from University of Eletro-ommuniations, Tokyo, Japan, in From 1978 to 6, he has been engaged in researh and development of seurity and multimedia devies, eletroni display for onsumer eletronis at SONY Corporation in Japan. In 9, he established ompany of CQ- S net In. Kanagawa, Japan. His researh interests inlude Internet of Things, radar tehnology, and signal and image proessing. Takuya Akiyama was reeived the B.E. degree from Tokyo University of Siene, Suwa, Japan, in 14. He is urrently working toward the M.S degree E = =.65 [V/m],.5 P = E z =.65 1π = [mw/m ]. 13

14 Open Journal of Internet of Things (OJIOT), Volume X, Issue X, XX Tomohiro Kobayashi was reeived the B.E. degree from Tokyo University of Siene, Suwa, Japan, in 15. He is urrently working toward the M.S degree. Naoki Ginoza is urrently working toward the B.E. degree at Tokyo University of Siene, Suwa, in Japan. Hideaki Matsue was reeived the B.S. and Ph.D degree from University of Eletroommuniations and Tokyo Institute of Tehnology, Tokyo, Japan, in 1978 and 1993, respetively. From 1978 to 4, he has been engaged in researh and development of digital mirowave radio-relay system, network arhiteture for personal ommuniation at NTT Eletrial Communiation Laboratories in Japan. He is urrently a Professor at the Tokyo University of Siene, Suwa, in Japan. His researh interests inlude Internet of Things, network arhiteture, and wireless ommuniation. 14