Global Navigation Satellite Systems
A Global Navigation Satellite System (usually referred to as "GNSS") is a constellation of satellites that emits radio-frequency signals. Tracking a minimum of three satellites allows a user receiver to compute its 2D-position, and four satellites allows a user receiver to compute a 3D-position in a global geodetic reference frame as well as velocity and time. The various GNSS signals can be differentiated by their frequency, modulation scheme, and navigation data that are transmitted.
Today, the following global and regional satellite navigation systems are operational or in its deployment phase:
Galileo will be Europe's global navigation satellite system, providing a highly accurate, guaranteed global positioning service under civilian control. It will be inter-operable with GPS and GLONASS, the two other global satellite navigation systems.
The United States Global Positioning System (GPS) is a space-based global navigation satellite system (GNSS) that provides reliable positioning, navigation, and timing services to civilian and military users on a continuous worldwide basis.
GLONASS (Russian: ГЛОНАСС, abbreviation of ГЛОбальная НАвигационная Спутниковая Система; tr.: GLObal'naya NAvigatsionnaya Sputnikovaya Sistema; "GLObal NAvigation Satellite System" in English) is a radio-based satellite navigation system operated for the Russian government by the Russian Space Forces. It is an alternative and complementary to GPS, the Chinese BeiDou navigation system, and the planned Galileo positioning system of the European Union (EU).
The BeiDou Navigation Satellite System (BDS), also known as Beidou-2, is a project by China to develop an independent global satellite navigation system. The BeiDou System is not an extension to the previously deployed Beidou-1, but a new GNSS similar in principle to GPS and Galileo.
Satellite Based Augmentation Systems
EGNOS, the European Geostationary Navigation Overlay Service is the first pan-European satellite navigation system. It augments the US GPS satellite navigation system and makes it suitable for safety critical applications such as flying aircraft or navigating ships through narrow channels.
The Wide Area Augmentation System (WAAS) is an air navigation aid developed by the Federal Aviation Administration to augment the Global Positioning System (GPS), with the goal of improving its accuracy, integrity, and availability. Essentially, WAAS is intended to enable aircraft to rely on GPS for all phases of flight, including precision approaches to any airport within its coverage area.
Multi-functional Satellite Augmentation System (MSAS) is a Japanese SBAS (Satellite Based Augmentation System), i.e. a satellite navigation system which supports differential GPS (DGPS) designed to supplement the GPS system by reporting (then improving) on the reliability and accuracy of those signals. Tests had been accomplished successfully, MSAS for aviation use was commissioned on September 27, 2007.
Regional Navigation Satellite Systems
The Indian Regional Navigational Satellite System (IRNSS) is an autonomous regional satellite navigation system being developed by Indian Space Research Organisation (ISRO) which would be under total control of Indian government. The requirement of such a navigation system is driven by the fact that access to Global Navigation Satellite Systems, GPS, is not guaranteed in hostile situations.
The Quasi-Zenith Satellite System (QZSS), is a proposed three-satellite regional time transfer system and enhancement for the Global Positioning System, that would be receivable within Japan. The first satellite 'Michibiki' was launched on 11 September 2010.
Other Regional Systems
GNSS satellites send their signals in a specific radio-frequency band. The signals are normally pseudo-random noise (PRN) spread-spectrum signals that are transmitted in micro-wave frequency bands. The receiver can separate the signal of each satellite, because of their individual and different code modulation. This technique is called Code Division Multiple Access (CDMA) and is used e.g. by GPS or Galileo.
By generating the same type of signal as a reference, a GNSS receiver can measure the so-called pseudo-range to the satellite, which resembles the geometric distance, contains clock biases of both, satellite and receiver, and other error components. The accuracy obtained with this pseudo-range measurement lies typically in the order of meters. For more accurate applications, a different type of observable, called carrier-phase measurement, can be used. This measurement is accurate to few millimeters, but is ambiguous with respect to wave-lengths of the signal. Hence, it needs to be exploited carefully. For determining velocity, also a doppler measurement - comparable to integrated carrier-phase - may be exploited. The quality of all measurements is driven by the received signal power, which is measured for each signal.
In addition, most of the signals contain encoded navigation data. These data contain information on the satellite's position and clock bias with respect to a common system reference frame as well as many other data that may be used by the receiver. The data related to the transmitting satellite are called ephemeris data.
The pseudo-range measurements together with ephemeris data allow the user receiver to compute its position, velocity and clock bias.
GPS simulation is part of the more general GNSS simulation. Here GPS signals are generated exclusively. As GPS is presently the most commonly used GNSS worldwide, it is of special economical relevance. The simulation of GPS signals is an industry standard today. It allows developing, integrating and testing GPS receivers as well as assessing their navigation performance. Stand-alone receivers or receivers integrated in devices like mobile-phones or complete integrated navigation systems can be tested.
Usually the GPS signal on L1 is simulated as it is the most frequently used civil signal, but there is also a wide range of navigation applications that require simulation of L2 or L5 signals, or SBAS (Satellite Based Augmentation Systems) signals in addition.
Special applications such as the testing of military or aerospatial receivers require the authentic generation of encrypted or otherwise "limited" signals as well as the depicting of specific user scenarios. IFEN offers cost effective solutions for all relevant requirements. Please refer to our GPS simulators NavX-NCS Essential and Professional or just get in contact with one of our experts.
In a multi-GNSS simulation several GNSS constellations with the signals of their satellites are simulated for a static or kinematic user. Realistic simulation covers all relevant aspects, like satellite orbits, clocks, ionospheric and tropospheric effects, and many other. Many Multi-GNSS simulators, like NavX-NCS Professional, allow also the simulation of GNSS "feared events" like sudden clock drifts or jumps or other potential faults.
From pedestrian over automotive and aeronautical applications up to space applications, today's GNSS signal generators are fully adjustable to the specific behaviour of any receiver motion, including its typical antenna patterns behaviour.
The most important difference to real multi-GNSS signals - no matter whether they might be generated by USA's GPS, Russia's GLONASS, the Japanese QZSS, PR China's BeiDou, European Union's Galileo, IRNSS of India or even future systems - is the full controllability, repeatability and recordability of the whole multi-GNSS scenario. This way, the same scenario can be run repeatedly to support any iterative development and testing activity and provide valuable performance results.
GNSS Fundamentals, Receivers and Applications
A Global Navigation Satellite System (GNSS) involves a constellation of satellites orbiting at about twenty thousand kilometers altitude over the earth surface, continuously transmitting signals that enable users to determine their three-dimensional position with global coverage.
GNSS Receivers process the Signals In Space (SIS) transmitted by the satellites, being the user interface to any Global Navigation Satellite System (GNSS). Even though the information provided by a generic GNSS receiver can be used by a wide range of Applications, most of them rely on the receiver's navigation solution - i.e. receiver computed Position, Velocity and Time (PVT).
GNSS applications are applications that use GNSS systems for their functionality. GNSS application use GNSS Receivers to collect position, velocity and time information to be used by the application. In some specific cases other measurements output by the receiver might be used. The receivers might be generic all purpose receivers or can be built specifically having the application in mind.
- Navipedia - http://www.navipedia.net/index.php/Main_Page
- GPS Status - http://www.navcen.uscg.gov/?Do=constellationStatus
- EGNOS Status - http://egnos-user-support.essp-sas.eu/egnos_ops/EGNOS_system/SIS_status
- WAAS Status - http://www.nstb.tc.faa.gov/index.htm
- GLONASS Status - http://glonass-iac.ru/en/GLONASS/
- US Coast Guard - http://www.uscg.mil/
- IGS - http://www.igs.org/
- Time References- http://www.leapsecond.com/java/gpsclock.htm
|AltBOC||Alternative Binary Offset Carrier|
|APV(-I)||Approach Procedure/Operations with Vertical Guidance|
|Advanced Receiver/Ranging Autonomous Integrity Monitoring|
|CDMA||Code Division Multiple Access|
|COTS||Commercial Off The Shelf|
|DOP||Dilution of Precision|
|EASA||European Aviation Safety Authority|
|ECEF||Earth Centered Earth Fixed|
|EGNOS||European Geostationary Navigation Overlay Service|
|ESA||European Space Agency|
|EUROCAE||European Organisation for Civil Aviation Equipment|
|Eurocontrol||European Organisation for the Safety of Air Navigation|
|FDMA||Frequency Division Multiple Access|
|GATE||German Galileo Test and Demonstration Environment|
|GDOP||Geometrical Dilution of Precision|
|GEO||Geostationary Earth Orbit|
|GLONASS||Globalnaja nawigazionnaja sputnikowaja sistema (Global Navigation Satellite System)|
|GNSS||Global Navigation Satellite System|
|GPS||Global Positioning System|
|GUI||Graphical User Interface|
|HDOP||Horizontal Dilution of Precision|
|HEO||High Earth Orbit and Elliptical Orbit|
|ID||Identification / identifier|
|IGSO||Inclined Geo-Synchronous Orbit|
|L1||L1-GPS frequency (L1 = 1575,42 MHz)|
|L2||L2-GPS frequency (L1 = 1227,2 MHz)|
|LEO||Low Earth Orbit|
|MSAS||Multi-functional Satellite Augmentation System|
|MEO||Medium Earth Orbit|
|NCS||Navigation Constellation Simulator|
|NMEA||National Marine Electronics Association|
|PPS||Pulse Per Second|
|PRN||Pseudo Random Noise|
|PRS||(Galileo) Public Regulated Service|
|PVT||Position, Velocity and Time|
|QZSS||Quasi-Zenith Satellite System|
|RTK||Real Time Kinematics|
|S/N||Signal to Noise Ratio|
|SoC||Statement of Compliance|
|SoW||Statement of Work|
|TCXO||Temperature Controlled Oscillator|
|TDMA||Time Division Multiple Access|
|TDOP||Time Dilution of Precision|
|TEC||Total Electron Content|
|UTC||Universal Time Coordinated|
|VDOP||Vertical Dilution of Precision|
|WAAS||Wide Area Augmentation System|