A Doppler Smoothing Filter using Carrier Phase and Application to RTK

Transcription

1 A Doppler Smoothng Flter sng Carrer Phase and Applcaton to RTK Byng-Hyn Lee, Konkk Unversty, Korea Gy-In Jee, Konkk Unversty, Korea Chan-Gook Park, Seol Natonal Unversty, Korea BIOGRAPHY Byng-Hyn Lee s a Ph.D stdent n Konkk Unversty. He receved hs MS.c degrees at Konkk Unversty n He s nterestng n Software GNSS recever, GNSS modernzaton, precse postonng, and Ant-Jammng technqe. Gy-In Jee s a professor of Electroncs Engneerng of Konkk Unversty. He receved hs Ph.D n System Engneerng from Case Western Reserve Unversty n Hs research nterests nclde Indoor GPS postonng, Software GNSS recever, GPS/Galleo baseband FPGA desgn, and Ant-Jammng technqe. Chan-Gook Park s a professor of School of Mechancal and Aerospace Engneerng of Seol Natonal Unversty. He receved hs Ph.D n Control and Instrmentaton Engneerng from Seol Natonal Unversty n Hs research nterests nclde the development of Inertal Navgaton Systems, GPS/INS ntegraton, low-cost IMU applcaton, postonng for Ubqtos Sensor Network and advanced flterng technqes. ABSTRACT Recently, n the feld of ITS (Intellgent Transportaton System), accrate and precse poston of a vehcle n the street s more demandng. They want to know whch lane a car s drvng n. The GNSS RTK cold provde ths accracy. Bt, n rban street, de to ts envronment, the conventonal code and carrer based RTK can t be a practcal solton. The Doppler measrement from GNSS recever cold be consdered as one more measrement to solve ths problem. A carrer smoothng of Doppler measrement sng Kalman Flter s proposed n ths paper. Ths carrer smoothng technqe for Doppler measrement can mprove Doppler measrement nose level, especally for low cost GNSS recever. For more robst RTK float solton, ths carrer smoothed Doppler measrement s nclded n doble dfferenced RTK measrement and the velocty estmaton performance s mch mproved. And the nnovaton and covarance of the smoothng flter s fond to be effcent n detectng carrer cycle slp. Feld test n rban area shows effectveness of sng carrer smoothed Doppler measrement n RTK for precse postonng of vehcle n the street. INTRODUCTION In order to get hghly precse poston n GNSS system, carrer phase measrements mst be sed. As known n [1], the resolton of carrer phase measrements s typcally better than 0.1mm. However, so as to se ths measrement, nknown nteger cycles of carrer phase shold be resolved. Ths nknown nmber s so called nteger phase ambgty. In the open sky envronment, ambgty can be resolved and satelltes are n lne-of-sght well. Bt n rban case there are many problems. Frst, nteger ambgty s rarely resolved. Most land vehcles drve n rban area, and there re many tall bldngs. These case severance of phase lock loop, and t appears as cycle slp. To se carrer phase measrement stably, contnty of phase trackng shold be garanteed. Second s mltpath. Carrer phase measrements are robst to mltpath. However code measrements have large mltpath error, t s reflected to poston error. Bt Doppler measrement has small nflence by mltpath than code measrement and s free from nteger ambgty Ths, Doppler s one of the necessary measrements for rban precse postonng. However, the nose level of Doppler measred by the low-cost GNSS recever s worse than srvey GNSS recever. Therefore, ths paper proposes Doppler smoothng flter sng carrer phase measrement to mprove postonng performance n rban area.

2 BENEFITS OF DOPPLER MEASUREMENTS AND POSITION SMOOTHING FILTER -60 Pont Postonng Reslts Conventonal RTK se code and carrer phase measrement for precse postonng. Precse postonng s for srvey land ntl now, so t s sed n open sky envronment. And for precse postonng, nteger ambgty shold be resolved. It means navgaton flter needs sccessve phase measrements. However rban area has freqent varaton of vsble satelltes by bldngs, so t s hard to measre phase measrements contnosly. Ths fxed solton s rarely calclated n rban. It means conventonal RTK s not practcal solton n rban envronment. In ths paper, Doppler measrements are sed for more robst and precse float solton. Typcally, sers are movng vehcles n rban. So velocty s one of the mportant nformaton. Taken together, we need relable sngle-epoch measrements and that enhances performance of velocty estmaton. And Doppler measrements are the meanng of amont of change. The eqaton s as below. f r B b I T V (1) s Where s wavelength; f s raw Doppler measrements of recever from satellte ; r s geometrc range rate; satellte clock drft; B s recever clock drft; I s onospherc delay rate; b s T s s tropospherc delay rate; V s calclaton error of satellte velocty; s recever nose. And the physcal expresson s defned n eqaton (2). Where, velocty; f h v V B (2) h s LOS (lne-of-sght) vector; v s recever V s satellte velocty; s onospherc, tropospherc delay rate, velocty error of satellte and recever nose. That s, Doppler measrement s drect measrement for velocty, and Doppler added navgaton flter can mprove performance of velocty estmaton [2] and more accrate velocty makes state predcton mproved. And poston smoothng flter [3] sng Doppler measrement can redce poston error n rban (Fgre 1). Ths smoothng flter se delta-poston estmaton. north error (m) LSQ 8-EKF Delta-Poston east error (m) Fgre 1. Poston doman smoothng n Standalone GPS In Ref. [3], delta-poston was estmated by ntegratng Doppler measrements n order to lower nose level. The npts of poston smoothng flter are solton of navgaton flter and delta-poston and poston smoothng flter s one of the fson flter. Ths fson flter gves smoothng effect n poston doman. Eqaton (3) shows doble dfferenced Doppler measrement. h v h v h v (3) k, l k k l l k, l, j, j, j j j And eqaton (4) represent the term of ser velocty of eqaton (3) h v h v h v (4) k, l k, l k k l l j j, j, j, j The left term of eqaton (4) means delta-poston. That s, delta-poston can be estmated sng doble dfferenced Doppler measrements drectly. And errors of satellte and recever are elmnated or redced becase t s doble dfferenced Doppler measrement. Ths Doppler measrements of sngle-epoch can provde relable delta-poston. DOPPLER SMOOTHING FILTER If the qalty of Doppler measrement s as mch precse as carrer phase, then delta-poston s accrate wthot Doppler smoothng flter. And almost precse postonng n rban area s for ITS (Intellgent Transport System). For the ITS, the prce of recever shold be cheap. Unfortnately Doppler measrement measred by low cost recever has low qalty than srvey recever. Ths Doppler smoothng flter was proposed n order to enhance qalty of Doppler. Doppler measrement s the meanng of delta range. And there s no nteger ambgty n tme dfferenced carrer

3 phase whch s the meanng of delta range too. So, Doppler measrement can be smoothed by carrer phase. Kalman flter s sed as smoothng flter. The eqaton s as below State predcton: 2 xˆk x k 1 k k 1 (5) dt P P Q (6) ˆk k 1 Table 1. Delta poston and velocty error RMS No smoothng Doppler smoothng Delta poston [cm] Velocty [cm/s] Measrement Update: K k Pk P R k (7) xˆ xˆ K z xˆ (8) k k k dopp k ˆ ˆ P (1 K ) P (9) k k k North[m] Delta Poston Estmaton No smoothng Doppler smoothng The beneft of Doppler smoothng s not only mprovng measrement qalty bt also cycle slp detecton. Montorng the dfference between Doppler and tmedfferenced carrer phase s one of the most famos technqe for cycle slp detecton. Ths resdals of Doppler smoothng flter can be the npt of cycle slp detecton modle. EXPERIMENTAL RESULTS The performance of Doppler smoothng flter was evalated by applyng to RTK. Fgre 2 shows the otlne of navgaton system of n ths paper. Measrements Process Doppler Smoothng (wth Carrer measrements) Poston Doman Poston Doman Smoothng ˆx xˆx, y, z, vx, vy, vz East [m] Fgre 3. Delta-poston error n statc Accordng to the reslts, the performance of delta poston and velocty estmaton s mproved sng Doppler smoothng flter. Ths means the qalty of Doppler measrements s mproved by carrer phase measrement. The followngs are the reslts n rban area. In ths dynamc envronment, tre poston s nknown. Ths the performance was evalated whether the reslts are n tre lane or not by sng precse map data and drvng n same lane. Fgre 4 shows rban envronment that srronded by bldngs and Fgre 5 shows precse map data of test ste. The magenta refers centerlne. Navgaton Flter PV model RTK Algorthm (Doppler Measrement Added to Navgaton Flter) ˆx DD, H DD Delta-Poston Estmaton (wth Doble-Dfferenced Doppler Measrement) Fgre 2. Otlne of navgaton system And the performance of velocty estmaton and delta poston estmaton are the evalaton ndces. Fgre 3 and Table 1 show the performance of delta poston and velocty estmaton n statc envronment. Fgre 4. Test ste (Urban)

4 LATITUDE n deg LONGITUDE n deg Fgre 5. Test ste (Precse map data) Table 2. Experment envronment Date 2011/03/21 Recever Baselne Performance analyss Reference: Novatel OEM-V Rover: U-blox AEK 4T 15km Precse Map Data Drvng twce n same lane Fgre 6 s the reslt of conventonal RTK n open sky envronment. In the open sky envronment, the reslts of conventonal RTK and poston smoothng flter are n tre lane. It means smoothed poston whch s calclated by Doppler measrement can be sed as precse postonng n rban envronment. And Fgre 7 s the reslt of velocty estmaton n rban area. In ths fgre, Doppler measrement added navgaton flter can provde more relable and stable velocty. Especally, after the lack of vsble satelltes s occrred, the estmated veloctes are jmped. However the Doppler added navgaton flter provdes more accrate veloctes RTK Delta-Poston RTK Delta-Poston LATITUDE n deg LATITUDE n deg LONGITUDE n deg Fgre 6. Postonng reslts n open sky [Straght Lane (left), Corner (rght)] LONGITUDE n deg

5 Fgre 7. Velocty reslts n rban area [wthot Doppler (left), Doppler added (rght)] LATITUDE n deg Fgre 8 shows postonng error of conventonal RTK n rban. Ths area s srronded by bldngs so mltpath cased ths poston error. In ths area, the tre trajectory s on the frst lane. Bt postonng error even ot of street s occrred wth conventonal RTK. Fgre 9 s the reslt of smoothed poston whch s calclated by proposed Doppler smoothng flter LONGITUDE n deg RTK Smoothng Flter LATITUDE n deg LONGITUDE n deg Fgre 9. Postonng reslts of Doppler smoothng flter appled By fgre 9, proposed method enables to redce poston error, n other word, postonng performance s mproved. Fgre 8. Postonng reslts of conventonal RTK n rban area (top) and ts envronment (bottom)

6 CONCLUSIONS The conventonal RTK cannot be a practcal solton n rban area becase t s hard to resolve nteger ambgty. In addton, the postonng error by mltpath and cycle slps s sgnfcant problem too. Bt n normal condton, RTK float solton can provde lane dentfable performance, and poston smoothng flter also can provde. There s postonng error, however, n rban area. Ths more mproved poston smoothng flter s needed. In ths paper, n order to mprove accracy and avalablty n rban, poston smoothng technqe sng smoothed Doppler measrement whch s smoothed by proposed Doppler smoothng flter. Proposed Doppler smoothng flter sng carrer phase mproves delta poston estmaton. It means proposed method can mprove the performance of poston smoothng flter and can provde more avalable postonng reslts. ACKNOWLEDGMENTS Ths research was spported by a grant from Transportaton System Innovaton Program (TSIP) fnded by Mnstry of Land, Transport and Martme Affars (MLTM) of Korean government. REFERENCES [1] Hofmann-Wellenhof, Lchtenegger, Wasle, GNSS Global Navgaton Satellte Systems, GPS, GLONASS, Galleo & more, Sprnger Wen NewYork, 2008 [2] Byng-Hyn Lee, Sng-Hyck Im, Gy-In Jee, Performance Analyss of GPS Standalone sng Carrersmoothed Doppler Measrement, GNSS Workshop, 2010, Jej [3] Helena Leppakosk, Jar Syrjarnne, Jarmo Takala, Complementary Kalman Flter for Smoothng GPS Poston wth GPS Velocty, ION GPS/GNSS 2003, Portland, OR [4] Byng-Hyn Lee, Gy-In Jee, Performance Analyss of GPS-RTK Floatng Solton wth Doppler Measrement, IS-GPS/GNSS 2010, Tape [5] L. Serrano, D. Km, R. B. Langley, A Sngle GPS Recever as a Real-Tme, Accrate Velocty and Acceleraton Sensor, ION GNSS 17th ITM, Sept. 2004, Long Beach, CA [6] Adeny Iyade, Real Tme Knematc GPS n an Urban Canyon Envronment, Map Asa Conference, 2005