Global Navigation Satellite System GNSS

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SPS b the new European satellite system Galileo c the modernized of US satellite system. GPS and d the reconstruction of Russian satellite system Glonass. The increasing demand for commercial location based services LBS has driven cellular phone. and network manufacturers to focus on positioning solutions which are even more accurate than. the regulatory mandates for positioning of emergency callers and other user services and. applications LBS projects aim to improve user friendly info mobility services for position. determination by combining wireless communications satellite navigation GNSS and. geographic information systems GIS based on a mobile client server architecture Lohnert et. The meaning of GNSS is the technical interoperability and compatibility between various. satellite navigation systems such as modernized GPS Galileo reconstructed GLONASS to be. used by civilian users without considering the nationalities of each system in order to promote. the safety and convenience of life GALILEO 2003 Feng 2003. Our interest here is to outline the new technologies and applications evolved and appeared from. the integration between the GNSS GIS and wireless communications. We will give an introduction of GNSS by introducing the characteristic of the three satellite. systems GPS GLONASS and Galileo signal structure receiver design math model of single. point positioning and differential positioning Wide area differential positioning such as WAAS. EGNOS and MSAS GNSS and wireless applications such as RTK network and LBS including. AVL and other services will be reviewed, Key Words Global Navigation Satellite System GNSS Global Positioning System GPS. GLONASS Geographic Information System GIS GALILEO LBS AVL Wireless Networks. WAAS EGNOS Applications of GNSS GIS to city planning and engineering. 1 INTRODUCTION, Satellite navigation systems has become integral part of all applications where mobility plays a. important role Heinrichs et al 2005 These functions will be at the heart of the mobile phone. third generation 3G networks such as the UMTS In transportation systems the presence of. receivers will become as common as seat belts or airbags with all car manufacturers equipping. their entry level vehicles with these devices, As for the past developments GPS launched a variety of techniques products and consequently. applications and services The milestone of satellite navigation is the real time positioning and. time synchronization For that reason the implementation of wide area augmentation systems. should be highlighted because they allow a significant improvement of accuracy and integrity. performance WAAS EGNOS and MSAS provide over US Europe Japan a useful. augmentation to GPS GLONASS and Galileo services Mulassano et al 2004. GNSS development has an interesting aspect due to its sensitive nature Considerable events or. developments are always subject to a couple of differentiators technological developments and. political decisions, GPS and Glonass in all stages of improvements are strictly related to those differentiators The. approval and startup of the European Galileo program is considered by far the most real. innovation Technological and political decisions in Galileo substantiate that interoperability and. compatibility must be reached in the forthcoming years Such issues are the true GNSS. improvement for the benefit of institutions and organizations. GNSS applications in all fields will play a key role moving its use from the transportation. domain to multimodal use outdoors and indoors It is expected that GNSS will increase. significantly the precision in position domain Lachapelle et al 2002. The concept of reference system for navigation is essential since all the applications of GNSS are. related to the coordinate system used The main application of GNSS is focused on the potential. of to determine the position in the Global reference system any where any time on the Globe in a. simple fast and cost effective manner, The integration between GNSS and other related technologies such as telecommunications.
GSM GPRS UMTS the Geographic Information Systems GIS and Inertial Navigation. System INS has created numerous applications that needs more time to be discussed in details. Many research efforts have been exerted in order to find each new applications to promote the. quality of our life using the GNSS benefits Lohnert et al 2001 Al Bayari and Sadoun 2005. 2 GNSS COMPONENTS, The GNSS consist of three main satellite technologies GPS Glonass and Galileo Each of them. consists mainly of three segments a space segment b control segment and c user segment. These segments are almost similar in the three satellite technologies which are all together make. up the GNSS As of today the complete satellite technology is the GPS technology and most of. the existing worldwide applications related to the GPS technology The GNSS technology will. become clearer after the operation of Galileo and the reconstruction of Glonass in the next few. 2 1 Global Positioning System, The United States Department of Defense DoD has developed the Navstar GPS which is an. all weather space based navigation system to meet the needs of the USA military forces and. accurately determine their position velocity and time in a common reference system any where. on or near the Earth on a continuous basis Wooden 1985. GPS has made a considerable impact on almost all positioning navigation timing and. monitoring applications It provides particularly coded satellite signals that can be processed in a. GPS receiver allowing the receiver to estimate position velocity and time Hofmann Wellenhof. et al 2001 There are four GPS satellite signals that are used to compute positions in three. dimensions and the time offset in the receiver clock GPS comprises three main components. Space segment The Space Segment of the system consists of the GPS satellites see Figure. 1 These space vehicles SVs send radio signals from space as shown in Figure 2. Control segment The Control Segment consists of a system of tracking stations located. around the world The Master Control facility is located at Schriever Air Force Base. formerly Falcon AFB in the State of Colorado USA, User segment The GPS User Segment consists of the GPS receivers and the user. community GPS receivers convert space vehicle SV signals into position velocity and. time estimates,GPS CONSTELLATION,L1 CARRIER 1575 42 MHz. C A CODE 1 023 MHz,NAV SYSTEM DATA 50 Hz,Modulo 2 Sum.
P CODE 10 23 MHz,L2 CARRIER 1227 6 MHz,21 SATELLITES WITH 3 OPERATIONAL SPARES. 6 ORBITAL PLANES 55 DEGREE INCLINATIONS GPS SATELLITE SIGNALS. 20 200 KILOMETER 12 HOUR ORBITS, Figure 1 GPS Constellation Figure 2 GPS Satellite Signales. The satellites are dispersed in six orbital planes on almost circular orbits with an altitude of about. 20 200 km above the surface of the Earth inclined by 55 degree with respect to the equator and. with orbital periods of approximately 11 hours 58 minutes half a sidereal day. The categories are Block I Block II Block IIR R for replenishment and Block IIA A for. advanced and a further follow on category Block IIF has also been planned ICD GPS 2003. Figure 3 shows the main GPS segments,Figure 3 GPS segments Aerospace Corporation 2003. 2 1 1 GPS Signals, The generated signals on board the satellites are based or derived from generation of a. fundamental frequency o 10 23 MHZ Hofmann Wellenhof et al 2001 The signal is. controlled by atomic clock and has stability in the range of 10 13 over one day Two carrier. signals in the L band denoted L1 and L2 are generated by integer multiplications of o The. carriers L1 and L2 are biphase modulated by codes to provide satellite clock readings to the. receiver and transmit information such as the orbital parameters The codes consist of a sequence. with the states 1 or 1 corresponding to the binary values 0 or 1 The biphase modulation is. performed by a 180 shift in the carrier phase whenever a change in the code state occurs see. Figure 4 The clear access code C A code and precision code P code are used for the satellite. clock reading both are characterized by a pseudorandom noise PRN sequence The W code is. employed to encrypt the P code to the Y code when Anti Spoofing A S is applied The. navigation message is modulated using the two carriers L1 and L2 at a chipping rate of 50 bps. Figure 4 Biphase modulation of carrier, It contains information on the satellite orbits orbit perturbations GPS time satellite clock.
ionospheric parameters and system status messages Leick 2003 The modulation of L1 by P. code C A code and navigation message D is done using the quadrature phase shift keying. QPSK scheme The C A code is placed on the LI carrier with 90 offset from the P code since. they have the same bit transition epochs For the L1 and L2 we have. L1 t a1 P t W t cos 2 f 1t a1C A t D t sin 2 f 1t,L 2 t a 2 P t W t cos 2 f 2 t. The signal broadcast by the satellite is a spread spectrum signal which makes it less prone to. jamming The basic concept of spread spectrum technique is that the information waveform with. small bandwidth is converted by modulating it with a large bandwidth waveform Hofmann. Wellenhof et al 2001, The generation of pseudo random sequence PRN in the code is based on the use of an. electronic hardware device called tapped feed back shift register FBSR This device can. generate a large variety of pseudo random codes but in this way the generated code repeat it self. after some very long time The receiver could distinguish the signals coming from different. satellites because the receiving C A code the Gold code has low cross correlation and is. unique for each satellite Leick 2003, The navigation message consists of 25 frames with each frame containing 1500 bit and each. frame is subdivided into 5 sub frames with 300 bit The information transmitted by the. navigation message is periodically updated by the control segment. 2 2 Modernized GPS, Due to the vast civil applications of GPS technology during the past decade or so and due to the. new technologies used in the satellite and receivers the U S government has decided to extend. the capabilities of GPS to give more benefits to the civil community In addition to the existing. GPS signals new signals will be transmitted by GPS satellite see Figure 5 Moreover this will. increase the robustness in the signals and improve the resistance to signal interference This. definitely will lead to a better quality of service QoS The new signals added to the GPS. Fontana et al 2001 are i a new L5 frequency in an aeronautical radio navigation service. ARNS band with a signal structure designed to improve aviation applications ii C A code to. L2C carrier L2 civil signal and iii a new military M code on L1 and L2 frequency for the. DoD has been added It has the potential to track signal even in poor conditions where the C A. code tracking on L1 would not be possible The new military code will be transmitted from the. Block IIR M and IIF satellites Betz 2002, It is well known that the presence of dual frequency measurements L1 and L2 has good.
advantages to eliminate the effect of the ionosphere and enhance the ambiguity resolution. especially for the high precision measurements Liu and Lachapelle 2002 High end civil dual. frequency systems will be based on L1 CA code and the newly designed L2 C code In the. coming few years the receivers will become more complex in order to allow tracking the new. civil code on L2 and tracking the encrypted P on L2 A S. The frequency of L5 is 1176 45MHz with chipping rate of 10 23 MHz similar to P code The. high chipping rate of L5 code will provide high performance ranging capabilities and better code. measurement than L1 C A code measurements Dierendonck and Hegarty 2000. L2 has a better correlation protection with respect to L1 since it has a long code This will be. useful in severe conditions where the GPS signals are weak such as navigation in urban indoor. and forested areas, The old codes and the new codes Millitary and civil on the L1 L2 and L5 need more. advanced modulation that better share existing frequency allocations with all signals by. increasing spectral separation and hence conserve the spectrum Consequently binary offset. carrier BOC is used for the Military code modulations Betz 2002. Figure 5 Modernized GPS signals,2 3 GLONASS, The GLONASS GLObal NAvigation Satellite System or GLObalnaya NAvigatsionnaya. Sputnikovaya Sistema is nearly identical to GPS Glonass satellite based radio navigation. system provides the positioning and timing information to users It is operated by the Ministry of. Defense of the Russian Federation GLONASS ICD 2002. Glonass space segment is consist of 24 satellites equally distributed in 3 orbit separated by 120 o. in the equatorial plane Satellite orbital altitude is about 19 130 km above the ground surface. This results in an orbital period of 11 15 44 corresponding to 8 17 of a sidereal day. The future of GLONASS seems uncertain due to economic problems facing the Russian. Federation The number of operational satellites was steadily decreasing over the past few years. The launch of three new GLONASS satellites in December 1998 was the first launch after a. lapse of 3 years, As of January 2006 a total of 10 GLONASS satellites are operational The oldest of the still. Key Words Global Navigation Satellite System GNSS Global Positioning System GPS Block IIR R for replenishment and Block IIA A for advanced and a further follow on category Block IIF has also been planned ICD GPS 2003 Figure 3 shows the main GPS segments Figure 3 GPS segments Aerospace Corporation 2003 GPS SATELLITE SIGNALS L2 SIGNAL Modulo 2 Sum Mixer L1 SIGNAL L1

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