A 24 GHz Band FM-CW Radar System for Detecting Closed Multiple Targets with Small Displacement

Transcription

1 A 24 GHz Band FM-CW Radar System for Deteting Closed Multiple Targets with Small Displaement Kazuhiro Yamaguhi, Mitsumasa Saito, Takuya Akiyama, Tomohiro Kobayashi and Hideaki Matsue Tokyo University of Siene, Suwa 5-1, Toyohira, Chino, Nagano, Japan CQ-S net In., Japan Abstrat In this paper, detetion method for 24 GHz band FM-CW radar system under losed multiple targets with small displaements environment is proposed, and its performanes are analyzed. The proposed detetion method was used a tunable FIR filter for signal proessing, and the distane and small displaement an be separated for eah target orretly from the reeived signal inluding all of signals from the targets at the FM-CW radar. Computer simulations were arried out for evaluating the proposed detetion method for FM-CW radar and analyzing the performane aording to the parameters under losed multiple targets environment. The results show that the proposed detetion method an detet both the distane and small displaement orretly under losed multiple targets environment. I. INTRODUCTION Radar systems with 24 GHz band is based on ARIB standard T73 [1] as sensors for deteting or measuring mobile objets for speified low power radio station. And the 24 GHz band radar system an be applied in various field suh as seurity, medial imaging and so on under indoor and outdoor environments. Various radar systems were reported [2], [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 24 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 this paper, in order to detet the distanes and displaements under losed multiple targets environment, we propose a detetion method for signal proessing with a tunable FIR filter in the FM-CW radar system. Furthermore, performane analysis for FM-CW radar system was shown in omputer simulations. This paper onsists of the following setions. In Setion II, we desribe the priniple of a FM-CW radar system under single target environment. In Setion III, we desribe the proposed detetion method under multiple targets environment. In Setion IV, we show the omputer simulations and analysis with the proposed FM-CW radar system. Finally, in Setion V, we onlude this paper. II. A. Priniple of FM-CW radar FM-CW RADAR SYSTEM FM-CW (Frequeny-Modulated Continuous-Wave) radar is a radar whih is transmitting a ontinuous arrier modulated by a periodi funtion suh as a sawtooth wave to provide range data shown in Fig. 1. Fig. 2 shows the blok diagram of a FM-CW radar system [9]. 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 [1] as shown in Fig. 1. 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 2πf 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 /15/$ IEEE 268 ICUFN 215

2 Fig. 1. Frequeny Signal proessing Fig. 2. Signal FFT Transmitted signal Time Sawtooth frequeny modulation D/A A/D VCO BPF BPF Tx Rx Blok diagram of a FM-CW radar system Reeived signal Target Target distane from the radar The refleted signal V R (f,x) is represented as V R (f,x) = Aα k γ k e jφk e j 2πf (2dk x), (2) where γ k and φ k are the refletivity 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 =, Eq. (2) is rewritten as V R (f,) = Aα k γ k e jφk e j 2πf (2dk). (3) The beat signal is generated as multiplying the transmitted signal in Eq. (1) and the reeived signal in Eq. (3) at the position x =. After through LPF, the output signal V out (f,) is generated by V out (f,) = A 2 α k γ k e jφk e j 4πfd k. (4) By using signal proessing, a distane and a displaement for the target are given from the generated output signal in Eq. (4). By using the Fourier transform, the distane spetrum of the output signal P (x) is alulated as follow. P (x) = = f+ fw 2 f fw 2 f+ fw 2 f fw 2 = A 2 K = A 2 K V out e 4πf j df A 2 α k γ k e jφk e j 4πfd k e f+ fw 2 α k γ k e jφk f fw 2 α k γ k e jφk e j 4πf (d k x) 4πfx j e j 4πf(d k x) df f w sin df 2πfw(d k x) 2πf w(d k x) The amplitude value of the distane spetrum P (x) in Eq. (5) is given as P (x) = A 2 α k γ k e jφk e j 4πf (d k x) sin 2πfw(d k x) f w 2πf w(d k x) K sin 2πfw(d k x) A 2 f w α k γ k, (6) 2πf w(d k x) and we have equality if and only if the phase omponents ϕ k + 4πf(dk x) about all of k are equal. Here, we assumed that the number of target is 1. The distane spetrum in Eq. (5) is rewritten as sin 2πfw(d 1 x) P (x) =A 2 α 1 γ 1 e jφ1 e j 4πf (d 1 x) f w, 2πf w(d 1 x) and the amplitude value of distane spetrum is given as sin 2πfw(d 1 x) P (x) = A 2 α 1 γ 1 f w. (8) 2πf w(d 1 x) This equation indiates that the distane for the target is generated by the amplitude value of distane spetrum. as The phase value of distane spetrum P (x) is represented P (x) =φ 1 + 4πf (d 1 x). (5) (7) = θ 1 (x). (9) 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. (1) If the phase value satisfies ϕ 1 =, Eq. (1) is rewritten as 3.11 [mm] d [mm] with f = [GHz]. That is, the small displaement of the target within ±3.11 [mm] is generated by the phase value of distane spetrum. 269

3 FM-CW radar 1m Distane Small displaement 1s 2.5mm Fig. 3. An example of FM-CW Radar for deteting human breathing FM-CW radar 2m 1m Power Time 2m Distane Small displaement 7.5s Time Phase 2.mm Small displaement: : 2.5 mm Period: 1. se Small displaement: : 2. mm Period: 7.5 se Fig. 5. Results of individual detetions for single moving target Fig. 4. Setup onditions with 2 targets + On the other hands, the maximum distane for measuring d max is f w f = [Hz], t w /t s d max = [m], (11) 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 = 124 µs and t s =1µs, the maximum distane is d max = 384 [m]. B. Detetion for single target In this setion, an example of detetion using the FM- CW radar system is demonstrated by using the omputer simulation. The setup ondition in the omputer simulation is shown in Fig. 3, and the ondition was orresponding to the experiment in [8]. We assumed that the FM-CW radar was loated on the eiling, and the target was the human who lie in bed. If there was only single target within the range of the FM-CW radar, the individual distane and small displaement was deteted orretly shown in Fig. 5. III. PROPOSED DETECTION METHOD 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 detetions for losed multiple targets, we propose the detetion method by using the signal proessing with a tunable FIR filter. The proedures of the proposed detetion method is as follow. We assumed that the FM-CW radar is loated a short distane from a bed as shown in Fig. 4. The radio waves are radiated from the FM-CW radar, and 2 targets lie on the bed. Fig. 6. Signal after A/D proess Fig. 7. Results of detetion for multiple moving targets Signal proessing FFT Peak position detetion Tunable band-path FIR filter Phase Display amplitude value Display phase value Blok diagram of the proposed detetion method in signal proessing The distanes from the radar to eah target are different, so that the peaks of distane spetrum are deteted at different frequeny. In this ase, the deteted result shown in Fig. 6 is sum of these 2 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 is used in the proposed detetion method. Figure 7 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 spetrum is obtained. After proessing the FFT operation, the peaks of amplitude value of the distane spetrum are alulated. 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. The tunable FIR filter has the enter frequeny orresponding to the alulated frequeny in the peak position detetions, 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 bandpath filter, the amplitude and phase value for eah target are deteted orretly. 27

4 [A.U.] Fig. 8. TABLE I. Parameters PARAMETERS IN COMPUTER SIMULATIONS Value Center frequeny f GHz Bandwidth of sweep frequeny f w 1, 2, 4, 8 MHz Sweep time t w 256, 512, 124, 248 µs Bandwidth for FIR filter Number of FFT points 496 Window funtion Maximal value for target 1: TABLE II. 2, 4, 8, 16, 32 Hz hamming SETUP CONDITIONS FOR TARGETS Parameters Distane 1. m 2. m of Displaement 2.5 mm 2. mm Period of displaement 1. s 7.5 s Minimal value: Maximal value for target 2: Beat frequeny [khz] (a) value Small displaement [mm] Phase value for target Time [s] (b) Phase value Definitions of evaluation values for omputer simulation IV. A. Setup ondition COMPUTER SIMULATION Deteted value Setuped value 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 I, and the parameters are based on ARIB standard T73 [1]. Center frequeny was GHz, and frequeny bandwidths were 1, 2, 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 256, 512, 124, and 248 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 2, 4, 8, 16, and 32 Hz. In the following setions, we desribe the evaluation values for analyzing the results of multiple targets detetions, and the performane analysis aording to bandwidth for sweep frequeny, sweep time, bandwidth for FIR filter, and position of target 2 are desribed. B. Evaluation values for amplitude and phase values Figure 8 shows the evaluation value for deteting the amplitude and phase values of the distane spetrum of multiple targets. We defined the degree of amplitude separation for amplitude value and 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], (12) where k denotes the number of target, S k denotes the degree of amplitude separation, P min denotes minimal value of ampli- Degree of amplitude separation [db] -1 2 Hz Bandwidth of sweep frewueny [MHz] 7.% 6.% 5.% 4.% 3.% 2.% 1.% Hz (a):.% Bandwidth of sweep frequeny [MHz] Fig. 9. Evaluation values versus bandwidth of sweep frequeny tude whose frequeny is f min, and P k denotes the peak value for k-th target with frequeny of f k. The for phase value is represented by = N d i d i 2 i=1 d i 2, (13) 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. C. Performane for Bandwidth of sweep frequeny Figure 9 shows the evaluation values versus the bandwidth of sweep frequeny f w for amplitude value in (a) 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), was about 2 % with the bandwidth of sweep frequeny f w = 1 MHz, and was also 271

5 Degree of amplitude separation [db] -1 2 MHz Hz Sweep time [us] (a): Degree of amplitude seperation [db] -1 MHz Bnadwidth of FIR filter [Hz] (a): 7.% 6.% MHz Hz 7.% 6.% MHz 5.% 5.% 4.% 3.% 4.% 3.% 2.% 2.% 1.% 1.%.% Sweep time [us].% Bandwidth of FIR filter [Hz] Fig. 1. Evaluation values versus sweep time Fig. 11. Evaluation values versus bandwidth of FIR filter improved as an inreasing the bandwidth of sweep frequeny. Although there was a few disadvantage for of target 2, the multiple targets detetions ould orretly ahieved beause the degree of amplitude separation with -1 db and with 6 % were enough values for deteting multiple targets in pratial use. D. Performane for Sweep time Figure 1 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 db in aordane not to the sweep time. The degree of separation for target 2 had -1 db during the sweep time t w = µs. In the ase with t w = 214µs, the degree of amplitude separation was almost db. That is, it was diffiult to detet the peak value of amplitude for target 2. Moreover, ompared to the result in (b), the worst for target 2 was about 4 % with t w = 248 µs. Beause the resolution for distane spetrum was dereased as an inreasing the sweep time, the sweep time should be less than 124 µs. E. Performane for Bandwidth of FIR filter Figure 11 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), for target 1 was less than 3 %, but for target 2 was more than 5 % with B = 16 and 32 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. F. Performane for distane between targets Finally, we show the result for deteting multiple targets when the target 2 omes lose to the target 1 from 2 m to 1.5 m. Figure 12 shows the evaluation values versus the position of target 2 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. 272

6 Degree of amplitude seperation [db] ( MHz) 6 ( MHz) 3 ( MHz) 4 ( MHz) 1 ( MHz) 2 ( MHz) Hz Position of target 2 [m] 7.% 6.% 5.% 4.% 3.% 2.% 1.% (a): ( MHz) 2 ( MHz) ( MHz) 2 ( MHz) ( MHz) 2 ( MHz) Hz.% Position of target 2 [m] Fig. 12. Evaluation values versus position of target 2 Compared to the results, the degree of amplitude separation and beome depleted as the target 2 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 = 2 MHz, the degree for target 2 was about -.3 db, and it was diffiult to detet the peaks. As shown in (b), when f w was less than 4 MHz, ould be kept about less than 5 %. However, in the ase with f w = 8 MHz, 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 other target s signal, and the imperfet FIR filter influened 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. V. CONCLUSION In this paper, a FM-CW radar system with 24 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 24 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. REFERENCES [1] ARIB STD-T73 Rev. 1.1, Sensors for Deteting or Measureing Mobile Objets for Speified Low Power Radio Station, Assoiation of Radio Industries and Businesses Std. [2] S. MIYAKE and Y. MAKINO, Appliation of millimeter-wave heating to materials proessing( speial issue reent trends on mirowave and millimeter wave appliation tehnology), IEICE transations on eletronis, vol. 86, no. 12, pp , de 23. [3] M. Skolnik, Introdution to Radar Systems. MGraw Hill, 23. [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. 52 6, 26. [5] T. Uebo, Y. Okubo, and T. Iritani, Standing wave radar apable of measuring distanes down to zero meters, IEICE TRANSACTIONS ON COMMUNICATIONS, vol. 88, no. 6, pp , jun 25. [6] T. SAITO, T. NINOMIYA, O. ISAJI, T. WATANABE, H. SUZUKI, and N. OKUBO, Automotive fm-w radar with heterodyne reeiver, IEICE transations on ommuniations, vol. 79, no. 12, pp , de [7] W. Butler, P. Poitevin, and J. Bjomholt, Benefits of wide area intrusion detetion systems using fmw radar, in Seurity Tehnology, 27 41st Annual IEEE International Carnahan Conferene on, Ot 27, pp [8] K. Yamaguhi, M. Saito, K. Miyasaka, and H. Matsue, Design and performane of a 24 ghz band fm-w radar system and its appliation, in Wireless and Mobile, 214 IEEE Asia Paifi Conferene on, Aug 214, pp [9] M. Skolnik, Radar Handbook, Third Edition. MGraw-Hill Eduation, 28. [1] W. Sediono and A. Lestari, 2d image reonstrution of radar indera, in Mehatronis (ICOM), 211 4th International Conferene On, May 211, pp