RESEARCH ON NEAR FIELD PASSIVE LOCALIZATION BASED ON PHASE MEASUREMENT TECHNOLOGY BY TWO TIMES FREQUENCY DIFFERENCE

Transcription

1 RESEARCH ON NEAR FIED PASSIVE OCAIZATION BASED ON PHASE MEASUREMENT TECHNOOGY BY TWO TIMES FREQUENCY DIFFERENCE Xuezhi Yan, Shuxun Wang, Zhongheng Ma and Yukuan Ma College of Communication Engineering Jilin Univerity Changchun, China Abtract: A new method to near field paive localization baed on phae hift meaurement technology by frequency difference i preented in thi paper. Near field paive localization accurately i a difficult problem all the while, epecially for a pecial ditance range neither long nor hort). In term of phyic ultraonic localization technology cannot be ued to near field paive localization becaue of it harp attenuation, o electromagnetic wave i the ole choice. TDOA Time Difference of Arrival ) method i of no effect ince time difference of arrival ignal can not be meaured accurately with conventional method on the condition of near field by reaon of electromagnetic wave velocity which i ame a light velocity. It i alo difficult for only uing traditional DOA Direction of Arrival) method to locate an object quickly and accurately under the ame condition for the ame reaon. The method on phae meaurement technology by two time frequency difference can olve the quetion perfectly.the principal interpretation,meaurement reult and error analyi of phae hift meaurement technology by frequency difference i preented in thi paper. Keyword: two time frequency difference, near field localization, phae hift meaurement electromagnetic wave. Introduction: Ditance meaurement i a traditional problem. For non contact meaurement there are two media ultraonic and electromagnetic wave that we can chooe to realize it. Ultraonic i a kind of mechanical wave o that it attenuate quickly when propagating in air. Generally ultraonic can meaure ditance le than 0 meter in air. Certainly there i another reaon that real time meaurement i impoible to achieve: for a moving object we can not meaure the accurate poition real time becaue it poition ha changed during the propagating time.comparing to ultraonic electromagnetic wave can meaure very long ditance uch a military radar do, however ince electromagnetic wave propagate a quickly a velocity 8 of light 0 m /, there will be a prodigiou abolute error for meauring a ditance directly with the time difference of arrival ignal when the ditance to be meaured i not very long <00m).Thu for a pecial ditance 50m 00m) neither ultraonic nor electromagnetic wave i fit to meaure it with the conventional method. A new method to near field paive localization baed on phae hift meaurement technology by two time frequency difference i preented in thi paper to olve the problem perfectly. It i eay to locate an object through triangle method if the ditance to two fixed receive port are obtained eparately o only the ditance meaurement i dicued in the paper. Reult: Ditance meaurement principal by meauring phae hift Ditance meaurement by phae hift i implemented by amplitude modulation electromagnetic ignal. Auming that the carrier frequency i f, the modulation waveform i howed in Figure, then the wavelength λ = c / f, c velocity of light. If ignal propagate from A to B, phae hift i preented a = mπ + = π m + m), ) Where m =0,,, m = / π

2 Figure. the waveform of ignal If the time for ignal propagating from A to B i t, ditance between A to B can be preented = ct = λ m + m) ) So if only the integral multiple m of period π and the reidual m in phae hift i meaured, the ditance can be obtained through the upper equation. Thu the electromagnetic wave wavelength λ can be eemed a a ruler. Phae hift meaurement technology can only meaure the reidual phae, thi i to ay the reidual m= / π can be obtained, but the integral multiple m of phae period π cannot be determined. So when the ditance meaured i long than wavelength the meaurement i not accurate, only when the ditance meaured i hort than wavelength the meaurement i accurate and the reult i howed λ = π ) If the ditance meaured i long comparatively,the modulation frequency can be depreed o a to make <, thu can be calculated accurately.. Electromagnetic wave phae detect technique )direct detection ruler frequency The detection ruler frequency f = c can derive from the detection ruler, i S f correponding to detection ruler length directly, namely the detection ruler length i determined by detection ruler frequency. Thi method i named a the direct detection ruler frequency mode. ) indirect detection ruler frequency In practice the ditance to be meaured i great generally o indirect detecton ruler frequency mode i adopted. Two modulation frequencie f and f are ued to meaure the ame ditance = = m m + m ) + m ) 4 ) The firt equation multiply through on both ide by through on both ide by f and the econd equation multiply, then ubtract the firt equation from the econd equation through on both ide and the formula convert to = [ m m) + m m)] = m+ m) 5 ) f

3 Where = = = f f 6 ) f = f f, m = m m, m = m ) m = π Here i a new detection ruler and f i the new detection ruler frequency according to S. and are the phae mantia which are meaured eparately when meauring the S ame ditance with f and f eparately ; the difference i equal to that i the phae mantia when meauring the ame ditance directly with a ingle frequency f f.thi i the baic principal of indirect detect ion ruler frequency method. = f )phae detect principal by frequency difference in active ditance meaurement c c f mater ocillator tranmit circuit fiducial ocillator mixer mixer receive circuit + phae detector Figure.Principal graph of phae detect by frequency difference Generally the active ditance meauring intrument by phae hift i adopting technology of phae detect principal by frequency difference.the principal of phae detect by frequency difference i howed in Figure. The ignal generating from the mater ocillator i modulated and ent out through tranmit circuit, it backtrack to the receive circuit after reflecting by the target through ditance. The original ignal and the receiving ignal are preented a the following two equation e = Aco t + ) 7 ) 8 ) 9 ) Where e B co t + + ) = denote phae hift, auming the ignal generated from the fiducial ocillator i : e = C co t + ) The ignal e i mixing with and in mixer and mixer eparately, then the output reference ignal e r e e and ditance meaurement ignal e are obtained from the two mixer ; they are preented a: e r = D co[ ) t + )] 0 )

4 e = E co[ ) t + ) + ] ) Thu we can meaure the phae difference of the two mixing ignal through phae detector. A concluion that the phae difference obtained by two low frequency ignal e and i equal to the phae difference obtained directly by the high frequency i drawn. Certainly the ditance information i preerved becaue the ditance i correponding to phae difference wholly. But to low frequency ignal the period i long comparatively o that the ame phae occupie more time o a to increae the meaurement preciion, therefore the ditance meaurement preciion i alo increaing, neverthele thi method doe not olve the meaurement range problem. To olve thi problem we propoed phae hift meaurement technology by frequency difference. 4)phae hift meaurement technology by two time frequency difference For a pecial ditance neither long nor hort, for example meter), range and preciion i the two factor that are needed to conider when chooing the meaurement frequency, now we will explain the relation between range and frequency through an example. Auming the maximum ditance i 00 meter the wavelength hould be λ 00 meter, now we chooe λ = 00m f =.5MHz ). Generally the tranmit antenna hould be longer than /0 wavelength of the electromagnetic wave at leat, half wavelength antenna i in common ue in engineering, hence, it i impoible to ue an antenna 00 meter long apparently. To olve the contradiction we chooe two ignal which frequency difference i.5mhz for example f = 50MHz and f = 48.5MHz )to meaure it imultaneouly, and it i feaible in practice, their phae difference i equal to the reult derived of the meaurement with.5mhz ignal directly. Now another quetion i of emergencehow to ue two ignal to meaure the ame ditance at the ame time? I.e. how to avoid the mutual interference? If the target object i tationary the quetion i imple, at firt the firt ignal f i tranmitted and then the econd ignal f i tranmitted after a fixed delay time t. If the target object i moving we till can tranmit ignal a the proce above on the condition that the object poition changed hardly during the fixed delay time t.uually the poition hift i mm level if t i m level, thi i to ay if the meaurement preciion i not greatly high the method i feaible. Figure and figure 4 are the principal graph of phae detect by two time frequency difference when the ignal frequency are and eparately. In a practical ytem receive circuit and four mixer and phae detector can be in common ue, only four fiducial ocillator are of independence. It i important to explain that the graph above i dead againt the paive ditance meaurement the tranmit circuit i eparate from the receive circuit in electronic, i.e. there i a eparate ignal tranmit ource, the receive circuit receive the ignal arriving directly no reflecting)) o that only the receive part are howed.to comprehend the principal graph better you can eem the receive circuit in figure a the mater ocillator in figure.in addition there are four mixer two mixer in figure ) in figure, thu it can improve the phae meaurement preciion. In figure the reult frequency and phae) of every tep i howed, and are obtained from figure and figure 4. = i the phae hift when we meaure the ditance with the frequency f = f f directly. Therefore the ditance can be calculated with formula ). Now it i neceary to interpret the meaning of two time frequency difference, the proce in Figure or Figure 4 i an integral proce of the firt frequency difference. Figure and Figure 4 are combined into one ytem, = i obtained by the econd frequency difference f f ) r e

5 receive circuit receive circuit Antenna, + fiducial ocillator, mixer mixer fiducial ocillator,, +, phae detector, Antenna mixer mixer4,, + Figure. Principal graph of phae detect by two time frequence difference when the ignal frequence i Antenna receive circuit receive circuit,, +, fiducial ocillator, mixer mixer fiducial ocillator4, mixer mixer4, 4 phae detector 4, + Antenna, Figure 4.Principal graph of phae detect by two time frequence difference when the ignal frequence i DicuionNow let ee an example, if the maximum ditance i 00 m, then f S =. 5MHz, auming f = S 50MHz and f MHz, deigned frequency of S = and 4 are 45MHz4.5 MHz MHz MHz, the ditance to be meaured i 05m, then = 0.5 π and π = are obtained from figure and figure 4, = ) π = 0.55 π if < then = + becaue λ < λ ), o the reult meaured i = = 05m. Certainly it i only an ideal ituation, it will generate error in a practical ituation.at preent the abolute error i 0.5 meter in thi ytem. The meaurement preciion i concerned with plenty of factor, in thi paper the influence of fiducially ocillator frequency value and preciion clock preciion and the conitency of mixer and phae detector are analyzed.. Frequency Value and preciion of fiducial ocillator determined the preciion of phae hift value and, for example if the econd level fiducial ocillator frequency i 4.8 MHz then the final frequency i = 0.MHz, if the econd level fiducial ocillator

6 frequency i MHz then the final frequency i = 0.00MHz, apparently if the digital phae detector intrument clock i uniform the phae detect preciion i elevated 00 time, certainly the higher the preciion i, the more difficult the technology i.if the ocillator preciion can not enure the meaurement preciion three level even four level frequency difference mode i adopted to olve it.. The clock preciion of the digital phae detector intrument ha great influence a uch. We till aume i equal to 0.00MHz, when the clock period i equal to 00 n and 0n eparately the counted number i 5000 and 5000, thu the ditance meaurement preciion i 0.04m00/5000) and 0.008m00/5000). So to improve the meaurement preciion the clock preciion hould be elevated if poible.. The conitency of mixer and phae detector hould be a higher a poible, thu the hardware error influence will be mall. It i one of the difficult point of thi method out of quetion. Concluion: The method of near field paive localization baed on phae meaurement technology by frequency difference preented in thi paper i differ from the traditional method, it elevate the meaurement preciion of near field paive meaurement greatly. There will be a great application propect along with the olving of everal key technique. Reference:. Sun changku, Ye henghua. aer Meaurement Technology. Tianjin Univerity Pre Dan li and Yu Hen hu. Energy-Baed Collaborative Source ocalization Uing Acoutic Microenor Array. EURASIP JASP 00:4 00) -7.. Joe C. Chen, Ralph E. Hudon, and Kung Yao, Maximum-ikelihood Source ocalization andunknown Senor ocation Etimation for WidebandSignal in the Near-Field IEEE TRANSACTIONS ON SIGNA PROCESSING, VO. 50, NO. 8, AUGUST 00