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GPS IN AVIATION SYSTEM

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  • 1. A.S.Adithya 131853 1
  • 2. Contents  History of Aircraft Navigation and Landing Systems  History of GPS in Aviation  GPS and Aviation Applications  GPS Landing and Navigation Systems (WAAS and LAAS) • Creating a better navigation system and eliminating errors  Effect of GPS in Aviation  Various Augmentation systems used worldwide  Literature Review  Case studies  References 2
  • 3.  1900’s -Pilots would land their planes in a field in the direction that gave them the best angle relative to the wind  1920’s -Lights and approach lighting  Radio navigation (Morse Code )  WWII-Radar  1980’s-Microwave landing systems (MLS)  1991- GPS began to be used  GPS was originally intended for the United States Military and Air Force  In June of 1991, portable GPS receivers began to be used in correspondence with autopilot  1994, the FAA halted further development of MLS and focused on making GPS the standard for navigation and landing. Brief History of Navigation and Landing Aids in Aviation 3
  • 4.  Commercial GPS aviation applications appeared in 1996  In 1998, Vice President Al Gore revealed plans to upgrade GPS with two new civilian signals for improved user accuracy and reliability, particularly with respect to aviation safety 4
  • 5. GPS and Aviation Applications  The satellites serve as a precise reference point  Aviation navigators, equipped with GPS receivers, use satellites as precise reference points to locate the aircraft's position anywhere on or near the earth  The distance from the receiver to the GPS satellites can be determined by estimating the amount of time it took the signal to reach the GPS receiver 5
  • 6. GPS Landing and Navigation Systems  There are two kinds of GPS landing and Navigation systems presently in place :  Wide Area Augmentation System (WAAS) &  Local Area Augmented System (LAAS) 6
  • 7. Wide area augmentation system (WAAS)  Basic GPS fails to meet the accuracy, availability, and integrity needed in navigation and landing of an aircraft  WAAS is based on a network of approximately 25 ground reference stations throughout the United States  Signals from GPS satellites are collected and received by the reference stations called wide area ground reference stations (WRSs) • Precisely placed reference stations receive GPS satellite signals and determine if any errors exist  WRSs linked to form the U.S. WAAS network  Accuracy from WAAs improves the positional accuracy 7 meters vertically and horizontally (Less than 3 Meters) 7
  • 8. Local Area Augmented System (LAAS)  A ground based amplification to GPS that focuses on a radius of approximately 20-30 miles from an airport  LAAS broadcasts its correction through a very high frequency radio data link from transmitter located on the ground  Accuracy of less than one meter in both horizontal and vertical axis compared to 15 years ago (100 Meter accuracy) • Problems with LAAS: System only offers a 20 to 30 mile radius of use while the WAAS is across the entire country  Potential for failure, which means that the system could be effected under weather conditions, solar activity, or jamming 8
  • 9. Creating a Better Navigation System and Eliminating Errors  Combine two common systems used in aircraft navigation, INS (Inertial Navigation System) and GPS  Neither system alone provides sufficiently accurate and complete time series of aircraft positions and velocities because of inherent technological problems  The INS allows accurate navigation with less than four satellites, helps reject multipath and aids the GPS in re-acquiring signals Errors:  The intermittent loss of satellite signals caused by the aircraft moving into or out of a satellite’s view, by an aircraft maneuver, or by the weather  Problems may occur during a turn. 9
  • 10. Effects of GPS in Aviation  Enhanced safety of flight throughout the region  Seamless navigation service based on a standardized navigation service and common avionics  More efficient, optimized, flexible, and user-preferred route structures  Significant savings from shortened flight times and reduced fuel consumption  Weather updates • Reduced costs to each individual State while increasing overall benefits to individual States and the entire region  Further economies from reduced maintenance and operation of unnecessary ground-based systems  Improved ground and cockpit situational awareness  Increased landing capacity for aircraft 10
  • 11. Various SBAS(Satellite- based Augmentation systems)used worldwide  European Geo-stationary Navigation Overlay Service(EGNOS)- European Union  GPS Aided Geo-Augmented Navigation System (GAGAN)- India  Multi-functional Transport Satellite (MTSAT) Satellite- based Augmentation System(MSAS)- Japan  StarFire & OmniSTAR are the commercial SBAS presently available. 11
  • 12. SBAS Status: Operational Systems  Wide Area Augmentation System (WAAS) – United States – Operational since 2003 – Supports en route, terminal and approach operations CAT I-like approach capability (LPV-200)  Multi-function Transport Satellite (MTSAT) Satellite-based Augmentation System (MSAS) - Japan – Operational since 2007 – Supports en route, terminal and non-precision approach operations 12
  • 13.  European Geostationary Navigation Overlay Service (EGNOS) – European Union – Open Service was declared in October 2009 – Safety-Of-Life Service has been operational since March 2011 – Supports En Route, Terminal and Approach operations - APV-1 (LPV equivalent) operational capability • Global Positioning System (GPS) Aided Geostationary Earth Orbit Augmented Navigation (GAGAN) - India – In development with plans for horizontal and vertical guidance – Final Acceptance Testing planned in 2012 13
  • 14. 14 GAGAN Fig.1. Various SBAS Systems Worldwide
  • 15. Literature Review  Abousalem et al. (2000) presented a study on the DGPS performance results using the newly modified receivers with the WAAS and EGNOS signals.  Ochieng et al. (2003) assesses the capability of GPS to provide the level of safety required for different aircraft flight navigation operations. It presents an analysis of the protection offered against potential catastrophic GPS failures at system and user levels. This is followed by an assessment of the different approaches to augmenting GPS for civil air navigation. Results show the inadequacy of GPS as a system for real-time safety critical use.  Witte et al. (2005) demonstrated accuracy of a WAAS-enabled GPS unit for the determination of position and speed. Comparison with the new and published data showed significant enhancements in both position and speed accuracy over a non-WAAS system. Position data collected during straight 15
  • 16. line cycling showed significantly lower sample-to-sample variation (mean absolute deviation from straight line 0.11 vs. 0.78 m) and greater repeatability from trial to trial (mean absolute deviation from actual path 0.37 vs. 4.8 m) for the WAAS-enabled unit compared to the non-WAAS unit.  Rao et al. (2007) discussed the implementation of the GAGAN-TDS (Technology Demonstration System). GAGAN TDS (Technology Demonstration System) is a forerunner for the operational Satellite Based Navigational System over the Indian region. The TDS phase of the project implements minimum set of elements for demonstrating the SBAS proof of concept over the Indian region.  Ettore et al. CIRA (2011) describes the algorithm implemented to process the broadcasted EGNOS SIS in order to obtain a position solution and integrity information compliant with RTCA DO229C. Moreover, they present test procedures and experimental results that may be used as a design guideline for monitoring manufacturing compliance and, in certain cases, for obtaining formal DO229C certification of equipment design and manufacture. 16
  • 17.  Jiwon Seo et al. (2011) studied aviation availability during a severe scintillation period observed using data from the previous solar maximum is analyzed. The effects from satellite loss due to deep fading and shortened carrier smoothing time are considered. Availability results for both vertical and horizontal navigation during the severe scintillation are illustrated. Finally,a modification to the upper bound of the allowed reacquisition time for the current Wide Area Augmentation System (WAAS) Minimum Operational Performance Standards (MOPS) is recommended based on the availability analysis results and observed performance of a certified WAAS receiver. 17
  • 18. Case Studies  1. Korean Wide Area Differential Global Positioning System Development Status and Preliminary Test Results -Ho Yun* and Changdon Kee, Doyoon Kim (Int’l J. of Aeronautical & Space Sci. 12(3), 274–282 (2011) DOI:10.5139/IJASS.2011.12.3.274) 18
  • 19.  Since 1999, the Korea has installed the NDGPS reference stations and has been providing local area DGPS service. Eleven coast reference stations and six inland reference stations cover the whole area of South Korea.  From 2003 to 2005, WADGPS research groups in SNU have developed the Korean WADGPS Test Bed (KWTB). The objectives of the KWTB are to develop the related essential technology, to verify the feasibility of Korean WADGPS. • The test bed consists of four WRSs (Wide-Area Reference Stations) and one WMS(Wide-Area Main Station). WRSs have been installed in the existing facilities of NDGPS reference stations.  Current Status:  WRS receives the measurements and navigation messages from the GPS receiver, and validates these data by quality monitoring.  WRS also plays an added role as a permanent test user for monitoring and analyzing performance of the demo system including accuracy, integrity, availability, and continuity. 19
  • 20.  WMS receives the raw data and WRS data from the multiple WRSs. After time synchronization of multiple WRS data, it checks the integrity flags and determines the optimal issue of data ephemerides (IODE).  WMS estimate the ionospheric grid point vertical delays As in Eq. , the ionospheric delay which is estimated from reference station contains receiver interfrequency bias (Rx IFB) and transmitter IFB (Tx IFB). 20 Subscript i means the i-th reference station and superscript j means the j-th satellite Tx IFB can be easily eliminated using time of group delay value, which is from GPS navigation data. Eq. is an Tx IFB compensated ionospheric delay
  • 21. 21 Fitting the ionosphere as spherical harmonics model,WMS estimates the Rx IFB of WRS. Eq. shows the second order spherical harmonics model.
  • 22. 22 Substituting , ionospheric delay and Rx IFB can be modeled as a function of local time and geomagnetic latitude. For estimating the Rx IFB in real time, Kalman filter has been implemented.The below Eqn has been used as an observation equation. Satellite orbit and clock errors are estimated using inverted GPS methods with Kalman filter After estimating the correction it generates the integrity information and SBAS messages.
  • 23. Korean WADGPS development plan  The main goal of this phase is to show the capability of Korean WADGPS using pseudolite and existing NDGPS infrastructures in real-time.This project is scheduled for 2010 to 2014.  According to this plan, after this project, Korea will launch a geostationary multifunctional satellite with a navigation payload which will be broadcasting augmenting signals.  This project is under active development to satisfy the following objectives: - Increased overall navigation performance (land/ air/marine, civil/military) - Independent & interoperable with other SBASs - Certified quality of service - Qualified for safety critical applications. 23
  • 24. 24 Fig.2. Milestones of Korean wide area differential global positioning system development.
  • 25. 25Fig.3.Project schedule (phase 2).
  • 26. Preliminary Test  To show the initial capability of KWTB, a preliminary test was conducted via simulation. Satellite orbit and clock errors were made by RINEX navigation files and precise orbit data from IGS SP3 files. • Satellite orbit and clocks calculated from SP3 are assumed as true. Ionospheric delay was generated from IONEX files. • The other error sources such as tropospheric delay or receiver noise were generated by accurate modeling. 26
  • 27. 27 Fig.4.Time history of satellite range errors. Fig.5.Histogram of satellite range errors for each PRN.
  • 28.  The history and the current status of the Korean WADGPS development plan is presented.  The Korean WADGPS development phase 1 has been successfully completed.  Phase 2 has just started, with the participation of one government office and seven research institutes and universities.  In this phase the technologies of the WADGPS ground system and pseudolite broadcasting system are secured.  In phase 3, Korea will launch multi-functional GEO satellites and initial operation of Korean SBAS will be started.  After this project, Korea will join the ranks of advanced countries in GNSS. 28
  • 29.  2. Modified Ionospheric Tomography algorithm using GAGAN data - D.Venkata Ratnam1, A.D. Sarma1, V. P.V.D. Somasekhar Rao and B.M.Reddy (The Journal of navigation )funded by ISRO ,Bangalore Vide Order No: CAWSES:05  Modeling of ionospheric delay is one of major challenges for GPS Aided Geo Augmented Navigation (GAGAN) system.  An attempt is made to characterize the Indian ionosphere using tomography technique. One of the prominent ionospheric tomography model is spherical harmonics model with Empirical Orthogonal Functions (EOF).  But it requires more number of coefficients. Therefore, the model is modified to reduce the coefficients.  The paper describes a 3-D ionospheric model, which is developed on the basis of tomographic techniques with GPS data. 29
  • 30.  Tomography refers to the cross-sectional imaging of an object from either transmission or reflection data acquired by illuminating the object from many different directions.  The modified tomograhic algorithm is tested using real time data over the Indian region.  The goal of ionospheric tomography is to find the electron distribution as a function of latitude, longitude and height in ionosphere.  The function based models have been chosen for development of ionospheric model. The reason for this is that they require less processing time and in turn would be useful in real time applications. 30
  • 31.  The TEC data is applied to tomographic algorithm to determine electron density with respect to latitude, longitude and altitude. TEC can be expressed in terms of electron density as,  TEC =∫N( r ) dl ( r ) where R(r) represents GPS receiver station. S(r) represents satellite N(r) represents Electron density dl(r) is unit length of altitudes Eq can be writeen in terms of electron density N(r) as 31 S( r ) R ( r )
  • 32.  ∫N(r)dl(r) ∫ Σ aΓ (h) Σb Y ( , )dl(r) 32 S( r ) R( r ) S( r ) R( r ) kk 1 1 where, Σa Γ(h) denotes EOFs k represents number of EOFs. q and f represent IPP longitude and latitude respectively. Σ b Y (q,f) , represents spherical harmonics function. bl is number of spherical harmonics coefficients. Eq is rewritten in terms of two variables as TECi=[Hi11 Hi12 …Hi1m Hi21……Hikl]x where, i is the number of TEC measurements k k 1 1
  • 33.  H =∫ Γ ( h ) .Y ( θ, φ) d l( r ) and  x=[a1b1 a1b2.........a kbl a2b1....................akbl]T  The design matrix [H] is formed using spherical harmonics and EOF functions.  Eq can be further approximated as 33 kl S( r ) R( r ) k 1
  • 34. or simply, TECi=Hx  We can estimate x (electron density) by least-square solution and reconstruct the ionosphere from basis functions with in terms of coefficients. Modified tomographic algorithm  In the modified tomographic algorithm the numbers of coefficients for obtaining electron densities are reduced.  Consequently, the amount of correction data to be transferred is reduced. In this, the design matrix (H) is modified tonon linear form. Eq can be expressed in non linear form as , 34
  • 35. 35 Finally the unknown coefficients can be estimated using either kinematic or Kalman filter. However, in this paper, linear least square estimator is used. • A 3-D modified ionospheric tomographic method has been described in this paper. The advantage of the function based model is that it requires less computational time for estimating ionospheric delays. • Accordingly, ionospheric corrections can be transferred within time to the user. • This technique indicates the occurrence of maximum electron density at thecrest region. • The accuracy of model is to be further validated using more data corresponding to several seasons.
  • 36. Summary  The Role of GPS in Aviation is a budding one and will only continue to grow as air travel becomes the main mode of transport in later years.  There are 3 operational SBAS (satellite based augmentation systems) in WAAS,EGNOS & MSAS and there are 2 which are nearing completion (GAGAN,Korean WADGPS) and many more in the pipeline in various contries.  GPS has become an integral part of the aviation industry and it’s importance will only continue to grow in coming years.  But is is not all rosy as GPS has some disadvatages too like it’s availability during strong ionospheric scintillation .  There is also the question of GPS Integrity and it’s impact on Aviaton safety but at the end of the day, the advantages it offers far outweigh it’s short-comings.  Many studies are being conducted and many new algorithms are being tested to overcome the short-comings and make GPS all the more better for aviation. 36
  • 37. References  Ettore De Lellis, CIRA (Centro Italiano Ricerca Aerospaziale)- An EGNOS Based Navigation System for Highly Reliable Aircraft Automatic Landing  Ho Yun* and Changdon Kee, Doyoon Kim (Int’l J. of Aeronautical & Space Sci. 12(3), 274–282 (2011) DOI:10.5139/IJASS.2011.12.3.274)- Korean Wide Area Differential Global Positioning System Development Status and Preliminary Test Results  Jitu Sanwale, Dhan Jeet Singh, U G Salawade(International Journal of Scientific & Engineering Research, Volume 4, Issue 12, December-2013 ) - The Global Navigation Satellite System (GNSS) and Indian Satellite Based Augmentation System (GAGAN)  Jiwon Seo,Todd Walter,Per Enge (IEEE VOL. 47, NO. 3 JULY 2011)- Availability Impact on GPS Aviation due to Strong Ionospheric Scintillation 37
  • 38. • K.N.Suryanarayana Rao,ISRO (IJRSP Vol.36,August 2007)-GAGAN- The Indian Satellite based Augmentation System • Mohamed Abousalem, Dr. Sergei Lusin, Mr. Oleg Tubalin, Mr. Javier de Salas(GNSS 2000 Conference, Edinburgh, Scotland, UK, May 1-4, 2000)- Performance Analysis of GPS Positioning Using WAAS and EGNOS  Rajat Acharya, Neha Nagori, Nishkam Jain, Surendra Sunda, Sawarmal Regar, M R.Sivaraman & Kalyan Bandopadhyay(Indian Journal of Radio Space Physics, Vol.36, Oct 2007, 394-404 pgs)- Ionospheric studies for the implementation of GAGAN  Suryanarayana Rao,Mr.A.S.Ganeshan,Mr.P.Soma,Dr.Surendra pal(ISRO) (58th International Astronautical Congress 2007)- GAGAN ( GPS AIDED GEO AUGMENTED NAVIGATION) - INDIAN SBAS SYSTEM • T.H. Witte, A.M. Wilson,(Journal of Biomechanics 38 (2005) 1717– 1722)- Accuracy of WAAS-enabled GPS for the determination of position and speed over ground 38
  • 39.  Venkata Ratnam, A.D. Sarma1, V. P.V.D. Somasekhar Rao and B.M.Reddy (The Journal of navigation )funded by ISRO ,Bangalore Vide Order No: CAWSES:05)-Modified Ionospheric Tomography algorithm using GAGAN data  Washington Y. Ochieng and Knut Sauer, David Walsh and Gary Brodin, Steve Griffin and Mark Denney (THE JOURNAL OF NAVIGATION (2003), 56, 51–65.)- GPS Integrity and Potential Impact on Aviation Safety 39
  • 40. Thanks for Listening ! 40

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