Gps

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2014

Daniyal Ali

BAT11362

4/2/2014

Global Positioning System (GPS)

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A Research on Global Positioning System

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Department of Engineering and Technology

Appropriate Task:

What is GPS? How it works?

A research on Global Positioning System (GPS). What is the working principle of GPS? What are the

advancement in GPS?

Prepared By:

Daniyal Al i (BAT11362)

Submitted To:

Prof . W/C Muhammad Shakeel

Discipline:

BS-Aviati on Technology

Submition Date:

02-04-2014

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Table of Contents

Cover Page

Table of Contents

Preface

Acknowledgement

GPS? A Brief Overview6

Usage of GPS6

How the Global Positioning System Works...6

How GPS Determines a Position7

Using a GPS Receiver10

Variants.14

References...18

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Preface

As Man is the best creature of AllahAlmighty. HE gave the emotions and intelligence to the Man. Man

has surplus over all the creatures by his intelligence. He is honored with this blessings to make his paths

in his life & to pursue his desires by following the right paths.

Everyone in this world is trying to pursue something. Some are trying to get best studies, some are in the

favor to earn more and more and some are those who want to do something to satisfy their utter one

desire. We are few of them.

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Acknowledgement

This project would not have been possible without the support of my professor. I wish to express my

gratitude to his supervision, Prof. W/C Muhammad Shakeel, who was abundantly helpful and

offered invaluable assistance, support and guidance. The knowledge about my project is really

interesting and technical. During this project i learnt many new things and different aspects of GPS.

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Global Positioning System (GPS)

GPS? A Brief Introduction:

In recent years, satellite navigation systems have revolutionized the concept of instrument

navigation. Developed as military systems by the United States and the Soviet Union, coupledwith the computer systems which have developed at the same time, they allow much moreaccurate and available position fixing for aircrew. ICAO refers to them as 'global navigationsatellite systems' or 'GNSS'.The United States system, called 'Global Positioning System', or GPS, is the most commonlyavailable. However, the Soviet, now Russian, 'Glonass' system is also commercially availablewith suitable receiver equipment. Receivers have been produced which can accept signalsfrom both systems, and other countries are considering developing new systems either on theirown or in conjunction with others.The Global Positioning System (GPS) is a satellite based navigation system that can be usedto locate positions anywhere on earth. Designed and operated by the U.S. Department of

Defense, it consists of satellites, control and monitor stations, and receivers. GPS receiverstake information transmitted from the satellites and uses triangulation to calculate a usersexact location.

Usage of GPS:GPS is used on incidents in a variety of ways, such as: To determine position locations; for example, you need to radio a helicopter pilot the

coordinates of your position location so the pilot can pick you up. To navigate from one location to another; for example, you need to travel from a lookout

to the fire perimeter. To create digitized maps; for example, you are assigned to plot the fire perimeter and

hot spots. To determine distance between two points or how far you are from another location.

How the Global Positioning System Works?The basis of the GPS is a constellation of satellites that are continuously orbiting the earth.These satellites, which are equipped with atomic clocks, transmit radio signals that containtheir exact location, time, and other information. The radio signals from the satellites, which aremonitored and corrected by control stations, are picked up by the GPS receiver. A GPSreceiver needs only three satellites to plot a rough, 2D position, which will not be veryaccurate. Ideally, four or more satellites are needed to plot a 3D position, which is much more

accurate.

Three Segments of GPSThe three segments of GPS are the space, control, and user

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Space SegmentSatellites orbiting the earthThe space segment consists of 29 satellites circling the earth every 12 hours at 12,000 miles inaltitude. This high altitude allows the signals to cover a greater area. The satellites arearranged in their orbits so a GPS receiver on earth can receive a signal from at least foursatellites at any given time. Each satellite contains several atomic clocks. The satellites

transmit low radio signals with a unique code on different frequencies, allowing the GPSreceiver to identify the signals. The main purpose of these coded signals is to allow the GPSreceiver to calculate travel time of the radio signal from the satellite to the receiver. The traveltime multiplied by the speed of light equals the distance from the satellite to the GPS receiver.

Control SegmentThe control and monitoring stationsThe control segment tracks the satellites and then provides them with corrected orbital andtime information. The control segment consists of five unmanned monitor stations and oneMaster Control Station. The five unmanned stations monitor GPS satellite signals and thensend that information to the Master Control Station where anomalies are corrected and sentback to the GPS satellites through ground antennas.

User SegmentThe GPS receivers owned by civilians and military

The user segment consists of the users and their GPS receivers. The number of simultaneoususers is limitless.

How GPS Determines a PositionThe GPS receiver uses the following information to determine a position.

Precise location of satellites

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When a GPS receiver is first turned on, it downloads orbit information from all the satellitescalled an almanac. This process, the first time, can take as long as 12 minutes; but once thisinformation is downloaded, it is stored in the receivers memory for future use.

Distance from each satelliteThe GPS receiver calculates the distance from each satellite to the receiver by using the

distance formula:Distance = velocity x time

The receiver already knows the velocity, which is the speed of a radio wave or 186,000 milesper second (the speed of light). To determine the time part of the formula, the receiver timeshow long it takes for a signal from the satellite to arrive at the receiver. The GPS receivermultiplies the velocity of the transmitted signal by the time it takes the signal to reach thereceiver to determine distance.

Triangulation to determine positionThe receiver determines position by using triangulation. When it receives signals from at leastthree satellites the receiver should be able to calculate its approximate position (a 2D position).The receiver needs at least four or more satellites to calculate a more accurate 3D position.

The position can be reported in latitude/longitude, UTM, or other coordinate system.

Sources of ErrorsThe GPS is not a perfect system. There are several different types of errors that can occurwhen using a GPS receiver, for example:

User mistakesUser mistakes account for most GPS errors; and a GPS receiver has no way to identify andcorrect these mistakes. Common examples of user mistakes include:

Inputting incorrect information into a GPS receiver, such as the datum, and whencreating a waypoint.

Unknowingly relying on a 2D position instead of a 3D position for determining

position coordinates. This mistake can result in distance errors in excess of amile. The signal from the satellite may be blocked by buildings, terrain, electronicinterference, and sometimes dense foliage. A GPS receiver needs a fairly clearview of the sky to operate.

The human body can cause signal interference. Holding a GPS receiver close tothe body can block some satellite signals and hinder accurate positioning. If aGPS receiver must be hand held without benefit of an external antenna, facing tothe south can help to alleviate signal blockage caused by the body because themajority of GPS satellites are oriented more in the earths southern hemisphere.

Multipath interferenceMultipath interference is caused by the satellite signal reflecting off of vehicles, buildings,

power lines, water and other interfering objects (Figure 5-2). Multipath is difficult to detect andsometimes impossible for the user to avoid or for the receiver to correct. When using a GPSreceiver in a vehicle place the external antenna on the roof of the vehicle to eliminate mostsignal interference caused by the vehicle. If the GPS receiver is placed on the dashboard therewill always be some multipath interference.

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Satellite and receiver clock errorsThese can be slight discrepancies in the satellites atomic clocks which may cause slightposition errors in the GPS receiver. Errors are monitored and corrected by the Master ControlStation.

Orbit errorsSatellite orbit pertains to the altitude, position, and speed of the satellite. Satellite orbits varydue to gravitational pull and solar pressure fluctuations. Orbit errors are also monitored andcorrected by the Master Control Station.

Satellite geometryThe location of GPS satellites in relation to a GPS receiver on the ground can impact thereceiversability to triangulate a 3D position. The quality of a receivers triangulated positionimproves the further apart GPS satellites are located from each other in the sky above thereceiver. The quality decreases if the satellites are grouped close together in the sky above thereceiver.

Atmospheric interferenceThe atmosphere can slow or speed up the satellite signal. Fortunately, error caused byatmospheric conditions (ionized air, humidity, temperature, pressure) has been reduced withthe implementation of the Wide Area Augmentation System (WAAS).

Selective Availability

Selective Availability is the intentional degradation (limits accuracy of satellite signals) of theGPS system by the U.S. Department of Defense for security reasons. At this time there is noSelective Availability in force; however, it can be reactivated without notice to GPS users.

Correction systemsCorrection systems have been designed to reduce some of the sources of error with GPS.

Real-time Differential GPSReal-time Differential GPS (DGPS) employs a second, stationary GPS receiver at a precisely

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measured spot, usually established through traditional survey methods (Figure 5-3). Thisreceiver corrects or reduces errors found in the GPS signals, including atmospheric distortion,orbital anomalies, Selective Availability (when it existed), and other errors. A DGPS station isable to do this because its computer already knows its precise location, and can easilydetermine the amount of error provided by the GPS signals. DGPS cannot correct for GPS

receiver noise in the users receiver, multipath interference, and user mistakes. In order forDGPS to work properly, both the users receiver and the DGPS station receiver must beaccessing the same satellite signals at the same time.

Wide Area Augmentation System

The Wide Area Augmentation System (WAAS) is an experimental system designed toenhance and improve aircraft flight approaches using GPS and WAAS satellites. The WAAScan be considered an advanced real-time differential GPS. It uses its own geo-stationarysatellites positioned over the equator to transmit corrected GPS signals to receivers capable ofreceiving these signals.Problems with WAAS include poor signal reception under dense tree canopy and in canyons,as well as decreased capability in northerly latitudes. Many GPS receivers are now capable ofreceiving the WAAS signal. However, WAAS should not be considered a consistently reliablesource for improving the accuracy of GPS until the technology improves.

Using a GPS Receiver

There are several different models and types of GPS receivers. Refer to the owners manualfor your GPS receiver and practice using it to become proficient.When working on an incident with a GPS receiver it is important to:

Always have a compass and a map.

Have a GPS download cable.

Have extra batteries.

Know memory capacity of the GPS receiver to prevent loss of data, decrease inaccuracy of data, or other problems.

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Use an external antennae whenever possible, especially under tree canopy, in canyons,or while flying or driving.

Set up GPS receiver according to incident or agency standard regulation; coordinatesystem.

Take notes that describe what you are saving in the receiver.

InputsEach time you use a GPS receiver, you will need to input information such as:

Position format units (example: UTM 11T 0557442m E 4836621m N).This input determines the way positions are displayed on the receiver screen. For example,sometimes you may want to use latitude/longitude coordinates and other times it may be betterto use UTM coordinates.

Map datum (example: WGS 84, NAD 27 and NAD 83).This input ensures that your GPS receiver and map are both using the same datum, which isextremely important for accuracy.

Distance units (feet, miles, meters).

Elevation units (feet or meters). North reference (true, magnetic, or grid).

Time format (12 or 24 hour) and time zone.

WaypointsA waypoint is a position based on geographic coordinate values, such as latitude/longitude andUTM, stored in the GPS receivers memory. They are sometimes referred to as landmarks.Once the waypoint is saved it remains static in the GPS receivers memory until edited ordeleted.

How Waypoints are Determined

A waypoint can either be a saved position fix or can be created by manually enteringcoordinates into the receiver.

To turn a position location into a waypoint is simply a matter of saving the receiverscurrent position as a waypoint. The receiver will give the position coordinates an alpha-numeric name or the user can designate a name. Once a position fix is saved, itbecomes a waypoint with static coordinates saved in the receivers memory.

Users can enter waypoints into the GPS receiver. For example, coordinates on a mapor coordinates radioed in from a remote location can be entered into a GPS receiver.

Naming WaypointsThe GPS receiver will automatically name waypoints with an alpha-numeric name; however, it

is best if you designate a unique name for each waypoint so you will know exactly what thewaypoint is referring to. Use short descriptive designations because long names can be hardto read when they are downloaded. You can make up your own names as long as you knowwhat they are. Some possible designations include:

D1, D2, D3 for different dozer lines

HL1, HL2, HL3 for different handlines

DP1, DP2, DP3 for different drop points

H1, H2, H3 for different helispots

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A1, A2, A3 for different access pointsRecord a description of each waypoint in your notes, otherwise it will be difficult to remember.

RoutesRoutes are just a sequence of waypoints (Figure 5-4). When navigating a route, the GPS

receiver will automatically change the destination waypoint to the next waypoint on the list as itreaches each waypoint.Once one waypoint is passed, the GPS receiver will navigate to the next waypoint. When aroute is first activated, the GPS receiver will assume that the first leg is A to B. B is thewaypoint being navigated to and A is the anchor point that defines the first leg of the route.

TerminologyThere is a lot of terminology associated with using a GPS receiver. Some of the commonterms are defined below and illustrated in following figure.

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Active from WaypointThis is the starting waypoint or the receivers last waypoint in an active route.

Active GOTO WaypointThis is the designated destination in the receiver, whether in an active route or as a singlewaypoint.

Active LegActive leg is always a straight line between the last waypoint and the GOTO waypoint. A GPSreceiver always plots the most efficient, straight-line course of travel between two pointstheactive leg. If the receiver is following a route, the active leg will be the desired track betweenthe last waypoint in the route, and the next waypoint in the route. If the receiver has deviatedfrom the route, the receiver selects the closest leg to its position and makes it the active leg inthe route (the next waypoint in the route list becomes the GOTO destination waypoint).

Bearing (BRG)/Desired Track (DTK)In GPS the term bearing is used instead of azimuth. As used in GPS, bearing is the compassdirection (expressed in degrees) from the present position to desired destination waypoint orthe compass direction between any two waypoints.

Course Deviation Indicator (CDI)This graphically shows the amount and direction of Crosstrack Error.

Course Made Good (CMG) or Course Over Ground (COG)This is the present direction of travel expressed in degrees from north. It is not necessarily themost direct path.

Crosstrack Error (XTE)This is the distance off the desired track (active leg) on either side of the active leg. Its thelinear difference between the Desired Track (DTK) and your actual Course Made Good (CMG).

Desired Track (DTK)This is a function of GOTO. It is shown in degrees from north. DTK is measured along theactive leg (a straight line between two waypoints in a route) or from your current position to a

designated GOTO waypoint, when not navigating a route. Estimated Position Error (EPE)

A measurement of horizontal position error in feet or meters based upon a variety of factorsincluding dilution of precision (DOP) and satellite signal quality.

Estimated Time En Route (ETE)The time left to destination based upon present speed and course.

Estimated Time of Arrival (ETA)The time of day of arrival at a destination

FixA single position with latitude, longitude (or grid position), altitude, time, and date.

GOTO FunctionThe GOTO function gives GPS receivers the capability of leading a person to any specifiedplace. Simply enter the coordinate of desired destination into the GPS receiver as a waypointand then, by using the GOTO function, tell the receiver to guide to destination. The receiverguides to destination using a steering screen. There are several different versions of a steeringscreen, but they all point in the direction needed to travel to from present position to thewaypoint selected.

GOTO WaypointIf traveling from one waypoint to another (using GOTO), then XTE will show the distance of

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deviation of your actual route from the active leg (a straight line) between those waypoints.

Speed Over Ground (SOG)This is the velocity you are traveling.

Tracking (TRK)/ Heading (HDG)This is the direction you are actually traveling or heading, expressed in degrees from north.

Track LogA track log is the GPS units record of travel or where you have been. As you move along, yourevery movement is being stored. Receivers with a TracBack feature will allow you to reverseyour route taking you back the same way you originally traveled. As you move along, mostGPS receivers show your track on a map screen.

Velocity Made Good (VMG)Velocity made good is the speed at which the destination is approached. If you are directly oncourse, VMG is the same value as SOG, but if you stray from course, VMG decreases and isless than SOG.

Variants GALILEO Satellite System

In 1998, the European Union (EU) decided to pursue a satellite navigation system independentof GPS designed specifically for civilian use worldwide. When com-pleted, GALILEO willprovide multiple levels of service to users throughout the world. Five services are planned:

An open service that will be free of direct user charges; A commercial service that will combine value-added data to a high-

accuracy positioning service. Safety-of-life (SOL) service for safety critical users; Public regulated service strictly for government-authorized users requiring

a higher level of protection (e.g., increased robustness againstinterference or jamming).

Support for search and rescue.

It is anticipated that the SOL service will authenticate the received satellite signals to assurethat they are truly broadcast by GALILEO. Furthermore, the SOL service will include integrity

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monitoring and notification; that is, a timely warning will be issued to the users when the safeuse of the SOL signals cannot be guaranteed according to specifications.

A 30-satellite constellation and full worldwide ground control segment is planned. Figuredepicts a GALILEO satellite. One key goal is to be fully compatible with the GPS system.Measures are being taken to ensure interoperability between the two systems. Primaryinteroperability factors being addressed are signal structure, geodetic coordinate referenceframe, and time reference system. GALILEO is scheduled to be operational in 2008.

Russian GLONASS SystemThe Global Navigation Satellite System (GLONASS) is the Russian counterpart to GPS. Itconsists of a constellation of satellites in medium Earth orbit (MEO), a ground control segment,and user equipment. At the time of this writing, GLONASS was being revamped and thesystem was undergoing an extensive modernization effort. The constellation had decreased to7 satellites in 1991 but is currently at 14 satellites. The GLONASS program goals are to have18 satellites in orbit in 2007 and 24 satellites in the 20102011 time frame. A new civil signal

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has been on orbit since 2003. This signal has been broadcast from two modernized satellitesreferred to as the GLONASS-M. These two satellites are reported to be test flight satellites.There are plans to launch a total of 8 GLONASS-M satellites. The follow-on satellite to theGLONASS-M is the GLONASS-K, which will broadcast all legacy signals plus a third civilfrequency for SOL applications. The GLONASS-K class is scheduled for launch in 2008. As

part of the modernization program, satellite reliability is being increased in both the GLONASS-M and GLONASS-K designs. Furthermore, the GLONASS-K is being designed to broadcastintegrity data and wide area differential corrections. Figures depict theGLONASS-M andGLONASS-K satellites, respectively. The Russian government has stated that, like GPS,GLONASS is a dual-use system and that there will be no direct user fees for civil users. TheRussians are working with the EU and the United States to achieve compatibility betweenGLONASS and GALILEO, and GLONASS and GPS, respectively. As in the case with

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GPS/GALILEO interoperability, key elements to achieving interoperability are compatiblesignal structure, geodetic coordinate reference frame, and time reference system.

Chinese BeiDou SystemThe Chinese BeiDou system is a multistage satellite navigation program designed to provide

positioning, fleet-management, and precision-time dissemination to Chinese military and civilusers. Currently, BeiDou is in a semi-operational phase with three satellites deployed ingeostationary orbit over China. The official Chinese press has designated the constellation asthe BeiDou Navigation Test System (BNTS). The BNTS provides a radio determinationsatellite service (RDSS). Unlike GPS, GALILEO and GLONASS, which employ one-way TOAmeasurements, the RDSS requires two-way range measurements. That is, a systemoperations center sends out a polling signal through one of the BeiDou satellites to a subset ofusers. These users respond to this signal by transmitting a signal through at least two of thesystems three geostationary satellites. The travel time ismeasured as the navigation signalsloop from operations center to the satellite, to the receiver on the user platform, and backaround. With this time-lapse information, the known locations of the two satellites, and an

estimate of the user altitude, the users location can bedetermined by the operations center.Once calculated, the operations center transmits the positioning information to the user. Sincethe operations center must calculate the positions for all subscribers to the system, BeiDoucan also be used for fleet management and communications. Current plans call for the BNTSto also provide integrity and wide area differential corrections via a satellite-basedaugmentation system (SBAS) service. At present, the RDSS capability is operational, andSBAS is still under development. The BNTS provides limited coverage and only supports usersin and around China. The BNTS should be operational through the end of the decade. In thelong term, the Chinese plan is to deploy a regional or worldwide navigation constellation of 1430 satellites under the BeiDou-2 program. The Chinese did not plan to finalize the design forBeiDou-2 until sometime in 2005.

Japanese QZSS ProgramAt the time of this writing, the Japanese were developing an indigenous satellite navigationaugmentation to the U.S. GPS under the QZSS program. The concept has been underdevelopment in Japan for more than 6 years and is the result of several independentgovernment and industry initiatives. Under current plans, the QZSS constellation will bedesigned to support both mobile communications and GPS augmentation services, but thesize and orbit remain incompletely defined. Specifically, the Japanese intend the navigationservices to address shortfalls in GPS satellite visibility in urban canyons and mountainousterrain, which the Japanese assess to be a problem in 80% of the country. In addition, theJapanese have expressed theneed for an independent regional navigation capability in times

of crisis in order toprotect the Japanese economy and its extensive use of GPS.Originally, the QZSS was an initiative of a joint industry effort under the (then) JapaneseCommunications Research Laboratory. A number of national and consortium projects in Japanhave developed concepts for a satellite-based augmentation to GPS with a funding andmarketing base broadened by providing both a navigation and a communications capability.The QZSS program appears to be the first such program to be moving forward with bothgovernment and industry support. The intent is to bring the navigation service on line in

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coordination with GPS upgrades. A U.S.-Japanese working group was established in October2002 and is working toward this goal. When the GPS-QZSS Technical Working Group met inJanuary 2004, problems related to interoperability were addressed through formal documentson configuration management.

References:1) Parkinson, B., A History of Satellite Navigation, NAVIGATION: Journal of The Instituteof Navigation, Vol. 42, No. 1, Spring 1995, pp. 109164.

2) GPS Joint Program Office, NAVSTAR GPS User Equipment Introduction, PublicRelease Version, February 1991.

3) NAVSTAR GPS Joint Program Office, GPS NAVSTAR Users Overview, YEE-82-009D,GPS JPO, March 1991.

4) McDonald, K., Navigation Satellite SystemsA Perspective, Proc. 1st Int. SymposiumReal Time Differential Applications of the Global Positioning System, Vol. 1,Braunschweig, Federal Republic of Germany, 1991, pp. 2035.

5) Global View, GPS World Magazine, February 2002, p. 10.

6) U.S. Department of Defense/Department of Transportation, 1999 FederalRadionavigation Plan, Springfield, VA: National Technical Information Service,December 1999.

7) https://gps.losangeles.af.mil/gpslibrary/FAQ.asp .8) Business in Satellite Navigation, GALILEO Joint Undertaking, Brussels, Belgium,

2003.9) http://www.geocaching.com.10)ANSER, Russias Global Navigation Satellite System, Arlington, VA, U.S. Air Force

Contract Number F33657-90-D-0096, May 1994.11)Kazantsev, V. N., et al., Overview and Design of the GLONASS System, Proc. of Intl.

Conference on Satellite Communications, Volume II, Moscow, Russia, October 1821,

1994, pp. 207216.12)Technical Description and Characteristics of Global Space Navigation System

GLONASS-MInformation Document, International Telecommunications Union,Documents 8D/46-E and 8D/ 46(Add.1)-E, November 22, 1994, and December 6, 1994,respectively.

13)On the Activity on Application of the Global Navigation Satellite System GLONASS, Russian Federation Governmental Decree 237, March 7, 1995, http://www.glonass-center.ru/decree.html.

14)Global Navigation Satellite SystemGLONASS, Interface Control Document (Version5.0), Moscow, 2002,http://www.glonass-center.ru/icd02_e.zip .

15)The Decree of the President of the Russian Federation, Decree 38 -RP, February 18,

1999,http://www.glonass-center.ru/38rp_e.html .16)Declaration of the Government of the Russian Federation, Russian FederationGovernmental

17)Decree 346, March 29, 1999, http://www.glonass-center.ru/decl_e.html.
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