다중신호원 (GPS/GLONASS) 기반전리층지연, 주파수간편이, 채널간편이, 그리고미지정수의분리추정 2012 년 10 월 한국항공대학교항공전자및정보통신공학부 최광호, 김희성, 이제영, 임준후, 이형근 * 참고문헌 (references) [1] 이형근, "GNSS 수신기망개발동향 ", 제어자동화시스템공학회지, Vol. 12, No. 1, pp. 47-51, 2006 [2] K. H. Choi, J. Y. Lee, H. S. Kim, J. R. Kim, and H. K. Lee, "Simultaneous Estimation of Ionospheric Delays and Receiver Differential Code Bias by a Single GPS Station," Measurement Science and Technology, Vol. 23, No. 6, Article # 065002, 2012 [3] H. S. Kim, J. Y. Lee, and H. K. Lee, "Estimation of Inter-Channel Bias and Ambiguity Resolution Strategy in GPS/GLONASS Combined RTK Positioning," Proceedings of IAIN World Congress, Oct. 1-3, Cairo, 2012 [4] H.S. Kim, J.Y. Lee, and H.K. Lee,"A Differential Reference Station Algorithm for Modular Decentralized GPS/GNSS Master Station Architecture," Proceedings of International Symposium on GPS/GNSS, Oct. 26-28, Taipei, 2010 [5] K. H. Choi, H. S. Kim, J. Y. Lee, J. H. Lim, and H. K. Lee, "Real-time Monitoring of Detailed Regional Ionospheric Activities by GPS CORS Networks," Proceedings of IAIN World Congress, Oct. 1-3, Cairo, 2012 [6] 이형근, "GAFAS: 정확성과안전성을위한 GPS 알고리즘 ", 2004 항공전자심포지엄논문집, Nov. 11, 2004 [7] GAFAS : GNSS Processing Software Modules for Accuracy and Safety, Attachment A, Report, APEC GNSS Implementation Team Meating, Seoul, Oct. 31- Nov. 3, 2005 [8] 이형근, 심주영," 실시간동적차분 GPS/GNSS 를위한소프트웨어 GAFAS 의성능분석 ", 2006 한국항행학회논문집, Oct. 19-20, pp. 273-278. [9] H.S. Kim, J.Y. Shim, H.K. Lee,"Designing a GPS Receiver Network with GNSS Algorithm for Accuracy and Safety," Paper #135, Proceedings of IGNSS 2007, 4-6 Dec., Sydney, Australia, 2007 [10] 김희성, 이제영, 이형근, "u-transportation 을위한저가단일주파수기반위성항법시스템의성능평가," 한국통신학회하계종합학술발표회, 2009 [11] 김희성, 이형근, " 차선별교통모니터링을위한위성항법수신기망설계및성능평가 ", 한국항행학회논문집, Vol 14, No. 2, pp. 151-160, 2010 [12] 김희성, 이제영, 박제두, 최광호, 이영준, 최종준, 김민우, 이형근," 국내 GPS/GNSS 상시관측소데이터의실시간통합활용방안연구 ", 제 17 차 GNSS 워크샾논문집, Nov. 4-5, 제주, 2010 2 1
미래위성항법인프라의개형 [1] Galileo Beidou GLONASS GPS 위성 1 위성 2 기준국수신기망 1 (GPS/Galileo, L1, L2, L5, 10 Hz) 주처리국 1 사용자수신기유형 1 VHF 안테나 1 사용자수신기유형 2 VHF 안테나 2 Uplink 안테나 1 Uplink 안테나 2 기준국수신기망 2 (GPS L1, L2, 1 Hz) 주처리국 2 정보융합센터 2 무결성 / 보정정보 1 무결성 / 보정정보 2 정보융합센터 1 3 발표내용 GPS 주파수간편이와전리층지연 [2] GLONASS 채널간편이의특성 [3] 실시간정밀전리층지도생성기법 [2,4,5] GAFAS 를활용한미지정수결정 [6-12] 향후연구방향 4 2
GPS 주파수간편이와전리층지연 [2] GPS 의주파수간편이, 코드바이어스, 군지연 주파수간편이 (Inter-Frequency Bias; IFB) 송신및수신회로하드웨어설계및구현에의하여발생함 코드와반송파에각각나타남 주파수에크게의존적임 GPS 의경우크게 4 가지종류로분류됨 위성코드 IFB 수신기코드 IFB 위성반송파 IFB 수신기반송파 IFB 코드바이어스 (Differential Code Bias; DCB) 코드 IFB 를달리표현하는용어임 위성 DCB 와수신기 DCB 로분류됨 군지연 (Group Delay; Tgd) GPS 위성에서방송하는항법메시지에포함되어있음 L1/L2 두주파수에달리적용되는전리층지연을보상하기위한목적임 Scaling 과 shift 에의하여위성 DCB 와등가한관계를가짐 6 3
단일기준국을활용한수직전리층지연과주파수간편이의분리추정 post-processing parts for performance evaluation real-time parts 7 단일기준국기반수직전리층지연추정의정확도 RMS differences of vertical ionospheric delay estimates between the proposed method and the interpolated IGS IONEX information (unit : TECU) from DoY 151 to 155 in 2011 8 4
단일기준국기반수직전리층지연의시간변화특성 9 IPP 별전리층변화에대한추정정확도비교 Comparison of the trends of the ionospheric delay estimates with respect to a satellite by the proposed method, the leveled carrier phase combination and the interpolated IGS IONEX information for (a) PRN 16 and (b) PRN 3, and their differences from leveled carrier phase combinations for (c) PRN 2 and (d) PRN 3 at the DAEJ station, DoY 155, 2011. 10 5
수신기 / 코드주파수간편이의추정정확도 Comparison of the receiver DCB estimated by IGS, CODE, ESA, JPL and the proposed method at DAEJ (left) and SUWN (right) stations on days from DoY 151 to 155 in 2011. 11 수신기 / 코드주파수편이추정의수렴성 Comparison of the receiver DCB estimates starting from three different initial values at DAEJ station (left, DoY 151 in 2011) and SUWN station (right, DoY 155 in 2011) 12 6
수신기 / 코드주파수간편이추정의정확도 Receiver DCBs estimates by the proposed method for five successive days from the DoY 151 to 155 in 2011 (unit: nanoseconds) 13 GLONASS 채널간편이의특성 [3] 7
다중신호원활용의장점 정확성, 가용성, 연속성, 신뢰성 가시위성의개수에의존함 특히가용성관점에서가시위성의개수증대가요구됨 GPS/GLONASS 다중신호원의활용 가시위성의개수증대에효과적임 15 다중신호원활용시고려사항 GPS/GLONASS 결합에있어서고려해야할사항 GPS 와 GLONASS 의중요한차이점 GPS GLONASS Reference Time UTC (USNO) UTC (SU) Reference Coordinate WGS-84 PZ-90 Generation of Signal CDMA FDMA 단독측위시기준시간및좌표계의차이를고려하지않을경우정확도의열화를가져옴 이중차분에의한정밀측위에있어서채널간편이가고려되지않을경우미지정수결정에영향을미침 16 8
GLONASS 채널간편이 채널간편이 (Inter-Channel Bias; ICB) 위성신호의구분을위하여 CDMA(Code Division Multiple Access) 원리를활용하는 GPS에비하여 GLONASS는 FDMA(Frequency Division Multiple Access) 원리를활용함 따라서 GLONASS는 L1/L2 두개의주파수를활용하는 GPS에비하여보다더다양한주파수를구분하여활용함 각위성과수신기내의각채널별회로는각기다른주파수를송수신해야함 따라서, 주파수에크게의존적인송수신회로의특성에의하여각채널별로각기다른지연값이발생하게됨 GPS에서발생하는주파수간편이는이중차분기법에의하여효과적으로제거될수있음 반면, GLONASS에서발생하는채널간편이는이중차분기법을적용하여도제거할수없는특성을가짐 17 동종수신기채널간편이의특성 영기저선 (zero Baseline) 실험 NovAtel DL-V3 잉여값이매우작음 채널간편이가효과적으로제거됨 Carrie-phase residuals & GLONSS frequency number (NovAtel & NovAtel) 18 9
이종수신기채널간편이의차이점 영기저선 (zero Baseline) 실험 NovAtel DL-V3 & Trimble NetR5 잉여값을크게발생시킴 최대잉여값이한파장의길이보다크게나타남 미지정수결정의성공률이크게열화됨 Carrie-phase residuals & GLONSS frequency number (NovAtel & Trimble) 19 채널간편이를고려하지않을경우미지정수의결정 영기저선 (Zero Baseline) 실험 NovAtel DL-V3 & Trimble NetR5 receivers 시점별미지정수결정 (Single Epoch AR) 적절하게모델링되지않은오차에의하여미지정수의결정이어려움 Fix Rate: 99.7 % Fix Rate: 11.4 % GPS only vs GPS/GLONASS RTK Result 20 10
채널간편이의시간영역변화특성 21 단일기준국 GLONASS 만을활용한수직전리층지연의추정 22 11
실시간정밀전리층지도생성기법 [2,4,5] 연구의필요성 전리층지연의추출에는주파수편이가불가피하게수반됨 전리층지연 / 주파수편이의분리를위하여기존의기술은중앙집중형시스템구조를활용함 (IGS IONEX, SBAS) 전리층지도의정확도는전리층정보가추출된기준점인 IPP(Ionospheric Pierce Point) 의개수에비례함 IPP의개수는참여기준국의개수에비례함 연산량부담으로인하여현행기술로는 IPP 및기준국개수를증가시키는데한계가있음 분산화된구조로정밀전리층지도를실시간에생성하는새로운방안이필요함 24 12
설계방향 각기준국이독립적으로전리층지연의절대값을추출할수있는방안의모색이필요함 전리층지연의상대값추출과는달리절대값추출에는주파수편이가수반됨 전리층지연과주파수편이의분리추정이필요함 고장검출및분리의용이성 각기준국 /IPP 에대하여추출된전리층지연값을효율적으로융합할수있는방안의모색이필요함 100 개이상의기준국활용가능함 다중신호원에대한확장성고려 5 TECU 내외의정확도 / 1 Hz 정도의출력주기 / 1 초이내의지연 전리층분포의이동을세밀하게관측 / 예측가능해야함 25 위성항법의주요변수 RTK : VRS, FKP, MAC ( 상대값필요, 정밀함 ) DD ionospheric delay, tropospheric delay, and integer ambiguity SD ionospheric delay (master satellite) SD tropospheric delay (master satellite) SD integer ambiguity (master satellite) SD receiver inter-frequency bias SD ionospheric delay, receiver differential code/carrier bias, tropospheric delay, and cycle ambiguity references for absolute values statistics modeling PPP, GPS Master Station ( 절대값필요 ) Absolute ionospheric delay, receiver/satellite differential code/carrier bias, cycle ambiguity, phase windup error, tropospheric delay, timing and ephemeris information 26 13
IPP 에서측정된전리층지연의공간보간개형 Vertical Iono. Delay for Each IPP IPP Interpolated Iono. Delay Surface Reference Station Reference Station SV/REC IFB Master Station 27 IGP(Ionospheric Grid Point) 의분포개형 Ionospheric Pierce Point (IPP) Ionospheric Grid Point (IGP) 28 14
제안된방식과 IGS 의기준점비교 proposed IGS TEC 전리층정보의기준점 29 정밀전리층지도의실시간생성을위한시스템구조 상시관측소별기준국수신기 IPP 별전리층추정 기준국 / 위성분리 DCB 기준국 / 위성 DCB 분리추정 GBAS/SBAS Maritime DGPS Land App. Space Weather A-GPS 보조정보 Dual Frequency Dual Frequency GPS Dual Receiver Frequency GPS Receiver GPS Receiver 지역전리층지도 방송궤도력의사거리누적위상 IGP 별수직전리층지연 Kalman Filter Kalman Filter Kalman Filter Kriging IPP 별수직전리층지연 기준국 / 위성결합 DCB Fusion Filter DCB : Differential Code Bias IPP : Ionospheric Pierce Point IGP : Ionospheric Grid Point 실시간전리층지도제공 IGP 별실시간전리층추정 Master Station 30 15
DM DM DM 마스터스테이션의상세구조 Master Station local state estimates SMleveled estimates DMleveled estimates regional IPP and VID estimates RIM SM SM SM SM SM SM Fusion differential integer ambiguities DM Fusion PSC PSC PSC PSC PSC RIM RIM IM SM : Standalone Module DM : Differential Module FM : Fusion Module PSC : Partial State Correction RIM : Regional Ionospheric Map IPP : Ionospheric Pierce Point VID : Vertical Ionospheric Delay IM : interface module 31 제안된방식과 IGS 전리층정보의특성비교 (1/6) 32 16
제안된방식과 IGS 전리층정보의특성비교 (2/6) 33 제안된방식과 IGS 전리층정보의특성비교 (3/6) 34 17
제안된방식과 IGS 전리층정보의특성비교 (4/6) 35 제안된방식과 IGS 전리층정보의특성비교 (5/6) 36 18
제안된방식과 IGS 전리층정보의특성비교 (6/6) 37 GAFAS (GNSS Algorithm For Accuracy and Safety) 를활용한미지정수결정 [6-12] 19
정밀측위를위한 SW 패키지 GAFAS 의구성 핵심모듈 인터페이스모드 측위모듈 Msg. Converter 통신모듈 Serial TCP/IP File 메시지모듈 RTCM 2.3/3.0 NMEA GAFAS Ntrip UBX Trimble (RT17) NovAtel SBF RINEX 2.1 측위모듈 Serial Interface Stream Receiver TCP/IP Interface Stream Server Stream Client Ntrip Client GAFAS Client GAFAS Server P2P Server P2P Client VRS File Interface RINEX Solution Real-Time Input: stream Post-Processing Input: RINEX Processing Mode Single Differential RTK float RTK Integer Position Mode Static Kinematic Kinematic Urban Correction Moving Base Real-Time Input: stream Post Processing Input: FILE RINEX RTCM to RINEX Receiver to RINEX RTCM 3.0 Receiver to RTCM RTCM to RTCM GUI 통신설정 메시지설정 측위모드설정 Filter Type RD Hatch Filter PD Hatch Filter Hybrid Filter Long Baseline 39 이동체를위한 GAFAS 의초기화메뉴 Main Window Communication Setting File Setting (Open/Create) TCP/IP Setting (with Ntrip Client) Serial Port Setting Plot 40 20
수신기망구현을위한 GAFAS 모듈 (a) 수신기망방송국 + 주처리국프로그램 프로그램흐름도 41 Filter Parameter 설정 Processing Mode Single/Differential/Float/Integer Positioning Mode Static/Kinematic/Urban/Correction Filter Type Hatch / Hybrid / Long baseline Filter Tropospheric Delay Model/TZD/TZD+Gradient Rate Ionospheric Delay Model/Vertical Iono. Delay Rate GLONASS Inter-Channel-Bias On/Off Stochastic Model (Measurement) Constant/CFTS/Empirical(elevation/baseline dependent)/adaptive RTK 측위 42 21
RTK 측위 Stochastic Model (Process Noise) 설정 Modeling Constant Inter-channel-Bias Random-Walk Tropospheric Delay Ionospheric Delay Inter-channel-Bias Gauss-Markov(1 st ) Tropospheric Delay Ionospheric Delay 43 RTK 측위 미지정수결정 주파수조합 (Frequency Combination) L1 only Widelane Ionofree(Narrowlane) Glonass 미지정수결정여부 Off (GPS Only) On GPS/GLONASS 미지정수결정 GPS first GLONASS later» GPS 미지정수결정» GLONASS Inter-channel-bias 결정» GPS/GLONASS 미지정수결정 44 22
# of Sat. RTZD (m) Correction Data 생성 기본설정 (Default Setting) Processing Mode Integer Positioning Mode Correction Filter Type Long Baseline Tropospheric Delay TZD Inter-Chnnel-Bias On (Constant) Stochastic Model (Measurement) Empirical General Option Reference(Rover) Position 설정 Rover Option 45 실험 : 중기선 (Medium Baseline) 측위 39 km Baseline 테스트 RTZD Estimate (39km baseline) 0.15 Float Integer 0.1 0.05 0-0.05-0.1-0.15 1 2 3 4 5 6 7 8 time (sec) x 10 4 10 9 8 Number of Satellites Total Widelane L1 7 6 5 4 3 2 1 0 1 2 3 4 5 6 7 8 9 time (sec) x 10 4 46 23
Error (m) 실험 : 중기선 (Medium Baseline) 측위 87km Baseline 테스트 1 0.5 0 ECEF XYZ Error & Standard deviation X Y Z std X std Y std Z -0.5-1 1 2 3 4 5 6 7 8 GPS Time (sec) x 10 4 47 실험 : 대류권및전리층지연보정데이터생성 파주 ( 국지원 ) 수원 ( 국지원 ) (59km) 수원 ( 국지원 ) 춘천 (NDGPS) (98km) 춘천 (NDGPS) 파주 ( 국지원 ) (90km) 48 24
채널간편이를고려한미지정수결정전략 GPS/GLONASS Measurements Ref. Rov. RTK Procedure EKF Baseline, DCB, ICB, N AR (GPS only) Fixed N (G) Baseline Float N (R) Residual Based ICB Search Float N (G/R) ICB Yes No Residual Based ICB Search Float N (R) ICB AR (GPS/GLONASS) Fixed N (G/R) Yes No AR (GPS/GLONASS) Fixed N (G/R) Fixed/Float Solution 49 실험개형 채널간편이를고려한영기저선정적실험 (1/3) Trimble NetR5 Splitter Choke Ring Antenna NovAtel DL-V3 50 25
채널간편이를고려한영기저선정적실험 (2/3) 실험조건 Sampling rate : 10 sec. Mask Angle : 10 deg. Processing Mode : Kinematic mode Measurements : L1 Code & Phase Ambiguity Resolution : Threshold=3, Single-epoch AR Zero Baseline Experiment Results (Float Solution) 51 채널간편이를고려한영기저선정적실험 (3/3) Zero Baseline Experiment Results (Fixed Solution) 52 26
채널간편이를고려한단기저선동적실험 (1/2) 실험조건 Reference Receiver Trimble NetR5 : Dual-Frequency Rover Receiver NovAtel DL-V3 : Dual-Frequency Mask angle : 10 deg. Sampling rate : 1 sec. Processing mode : Kinematic mode Measurements : L1 Code & Phase Maximum Baseline : 430 m Ambiguity Resolution Threshold of Ratio: 3 Validation: residual test, ratio-test Duration of multiple-epoch validation: 5 epochs 53 실험결과 채널간편이를고려한단기저선동적실험 (2/2) Fix Rate: 0.0% Fix Rate: 97.8% Short Baseline Kinematic Experiment Results (Fixed Solution & ICB) 54 27
결론및향후연구방향 Findings (1/3) 고려사항 실시간성 (real-time capability) 시간지연없이전리층, 주파수편이, 채널간편이을분리추정하는것이바람직함 모듈화 (modularity) 및다중화의편의성 (ease of redundancy) 고장을대비하여간편하게다중화할수있는특성이바람직함 자율성 (autonomy) 외부보조정보에의존하지않고자체적으로전리층, 주파수편이, 채널간편이을추정하는것이바람직함 (ex: IGS 정밀궤도력, IGS 전리층정보, MSAS 전리층정보등 ) 자율적으로생성된전리층정보와외부보조정보를융합할경우추가적인성능의향상을얻을수있음 56 28
Findings (2/3) 주파수간편이, 채널간편이 전리층지연의절대값을추정하고자할경우주파수간편이와채널간편이의분리추정은필수적임 전리층지연의상대값과 RTK를고려할경우 GPS 주파수간편이는이중차분에의하여효과적으로제거가능 반면, GLONASS 채널간편이는이중차분에의하여제거되지않으므로별도의고려필요 57 Findings (3/3) 거리영역평활화, 상태변수영역평활화, Phase-Leveling 단순한거리영역평활화는전리층지연추정의정밀도를향상시킬수있으나가관측성향상에기여하지않으므로주파수간 / 채널간편이의분리추정에도움이되지않음 Phase-leveling은거리영역평활화에비하여정밀도를극대화할수있으나거리영역평활화의경우와마찬가지로가관측성향상과실시간구현에난점이있음 상태변수영역평활화는정밀도 ( 평활화 ) 와정확도 ( 가관측성 ) 를동시에향상할수있음을확인함 58 29
결론 넓은영역에서의전리층의활발한운동에의하여유기되는비정상적전리층지연분 포를제한된차수의기저함수로모델링하기에는난점이있음 GPS 와 GLONASS 를포함한다중신호원을활용하여전리층지연을추정하고자할 경우전리층지연, 주파수간편이, 그리고채널간편이등분리추정해야할상태변 수가많음 수신기 / 위성혼합주파수간편이, 수신기 / 위성혼합채널간편이, 그리고수직전리 층지연은단일수신기만을활용하여도이론적으로분리추정이가능함 상시관측소인프라를활용하여측정점의개수를늘리는경우전리층지연추정의정 확도와정밀도를동시에향상시킬수있음 59 향후보완방향 기존의중앙집중형전리층추정방식의보완개선 보완개선된중앙집중형방식과과분산형방식의전리층추정성능 / 특성비교 전리층지연추정정밀도의향상과자율성보장을위해서는 IGS 정밀궤도력에 의존하지않고 100 km 이상장기저선에대하여안정적인미지정수결정필요 실시간구현후장기간의시험운영을통하여신뢰성있는통계적성능지표의 추출이필요함 60 30
경청해주셔서감사합니다 61 31