Transcript
GPS Trainer ST2276
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Operating Manual Ver 1.1
An ISO 9001 : 2000 company
94-101, Electronic Complex Pardesipura, Indore- 452010, India Tel : 91-731- 2570301/02, 4211100 Fax: 91- 731- 2555643 e mail :
[email protected] Website : www.scientech.bz Toll free : 1800-103-5050
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GPS Trainer ST2276 Table of Contents 1.
Introduction
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Experiments to be performed : Experiment 1 Understanding the principle of GPS Technology
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Experiment 2 12 a. Understanding the principle of GPS Satellite b. Understanding the generation of L1 carrier frequency. c. Understanding the operation of GPS Receiver. d. Establishing the link between the GPS Satellite and GPS Trainer.
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Experiment 3 a. Understanding the shape of Earth. b. Measurement of latitude, longitude.
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Experiment 4 a. Understanding the principle of PRN code in GPS. b. Understanding the principal of autocorrelation in GPS.
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Experiment 5 a. Understanding the principle of Geometry of the Satellite. b. Understanding the importance of PDOP, HDOP, and VDOP.
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Experiment 6 a. Understanding the principle of NMEA 0183 protocol. b. Analysis of NMEA 0183 protocols
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Experiment 7 Study of other NMEA Sentence
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Experiment 8 Study of the complete GPS Environment.
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GPS Quiz
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GPS Glossary
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GPS Acronyms
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Warranty
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List of Accessories
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Introduction Have you ever been lost and wished there was an easy way you needed to go? Ever find that perfect fishing or hunting spot and not been able to remember how to get back to it easily? How about finding yourself out hiking and not knowing which direction you should go to get back to your camp or car? Ever been flying along and needed to locate the nearest airspace you were in? Maybe you've been faced with the fact that it's time to pull over and ask someone for directions. Global Positioning System technology is rapidly changing how people find their way around the earth. Whether it is for fun, saving lives, getting there faster, or whatever uses you can dream up, GPS navigation is becoming more common everyday.
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Hi RoHS Compliance Scientech Products are RoHS Complied. RoHS Directive concerns with the restrictive use of Hazardous substances (Pb, Cd, Cr, Hg, Br compounds) in electric and electronic equipments. Scientech products are “Lead Free” and “Environment Friendly”. It is mandatory that service engineers use lead free solder wire and use the soldering irons upto (25 W) that reach a temperature of 450°C at the tip as the melting temperature of the unleaded solder is higher than the leaded solder.
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Experiment 1 Objective : Understanding the principle of GPS Technology Theory : The Global Positioning System (GPS) is and earth orbiting-satellite based navigation system. GPS is an operational system, providing users worldwide with twenty-four hour a day precise position in three dimensions and precise time traceable to global time standards. GPS is operated by the United States Air Force under the direction of the Department of Defense (DoD) and was designed for, and remains under the control of, the United States military. While there are now many thousands of commercial and recreational civil user’s worldwide, DoD control still impacts many aspects of GPS planning, operation, and use. Primarily designed as a land, marine, and aviation navigation system, GPS applications have expanded to include surveying, space navigation, automatic vehicle monitoring, emergency services dispatching, mapping, and geographic information system georeferencing. Because the dissemination of precise time is an integral part of GPS, a large community of precise time, time interval, and frequency standard users has come to depend on GPS as a primary source of control traceable through the United States Naval Observatory to global time and frequency standards. History of GPS : Developed in the 1960s, the Navy Transit satellite navigation system still provides some service as a two-dimensional (horizontal) positioning system. Good (200 meter) Transit positioning requires knowledge of the user altitude as well as a model of user dynamics during the fix, a process of integrating satellite signal Doppler shifts (the change in received signal frequency caused by the changing range) during the fly-over of the satellite. Another Navy system, based on the Timation satellites carried stable clocks (quartz, rubidium, and cesium) over the course of the program in the 1960s and 70s and was the precursor to the precise time capabilities of GPS (Easton 1978). GPS began in 1973 as a test program using ground-based transmitters at the U. S. Army Proving Ground at Yuma, Arizona, later augmented with early versions of GPS satellites first launched in 1978. During the 1980s, GPS, although not yet fully operational and requiring careful planning for missions during times of satellite availability, was increasingly used by both military and civilian agencies. Land, air, and sea navigation, precise positioning, carrier phase survey techniques, and precise time and frequency dissemination were all accomplished to a limited extent during the initial phases of GPS deployment (Klepczynski 1983). By 1989 ten development satellites, termed Block I satellites, had been successfully launched. By 1990, 43 laboratories requiring precise time were using GPS to synchronize their atomic clocks (Clements 1990). By 1994, 24 Block II and IIA operational GPS space vehicles (SVs) had been launched. The Block IIA SVs can store up to 14 days of uploaded data in case contact is lost with ground stations and can operate for 180 days with degraded navigation receiver performance. The next generation of space vehicles, the Block IIR SV s will incorporate changes to include the capability of maintaining precise time keeping without Control Segment uploads for periods of up to 210 days by exchanging data between GPS SV s (Rawicz, Epstein, and Rajan 1992). Scientech Technologies Pvt. Ltd.
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In December of 1993, GPS reached Initial Operational Capability, with a minimum of 24 satellites in orbit. On July 17, 1995 the Air Force announced that GPS had met all requirements for Full Operational Capability with 24 Block II SVs in orbit. With over 50 companies supplying a selection of over 275 GPS receivers to a global market, the well established user community of navigators, surveyors, geologists, geodesists, time and frequency users, and many thousands of recreational user has come to accept GPS as a viable military and civilian system. Civil and Military GPS : While controlled and maintained by the DoD, the GPS user community has a large civil component. In the 1977 National Plan for Navigation, published by the U. S. Department of Transportation (DoT), the NAVSTAR GPS user community was planned to include 27,000 military receivers. While the potential for a civil-sector user base was recognized, the document did not include plans for a civil GPS service (U.S. DoT 19773-14; 3-15). A decade later the Federal Radio navigation Plan (FRP) (U.S. DoD and DoT 1986) stated that GPS would be available to civil users, worldwide, on a continuous basis but with accuracy limited to 100 meters (95 percent). In these radio navigation documents position accuracy is usually specified as a two standard deviation (95 percent) radial error or 2drms (2 distance root mean squared) uncertainty estimate. For GPS the 95 percent probability and 2drms accuracy are equivalent (DoD and DoT 1995, A-2). The 1985 Comprehensive Global Positioning System User Policy defined both a military, encrypted, Precise Positioning Service and a "lower level of accuracy" Standard Positioning Service (U.S. DoD and DoT 1986, B-32). Standard Positioning Service : The Standard Positioning Service (SPS) is defined in the most recent FRP as: the standard specified level of positioning and timing accuracy that is available, without restrictions, to any user on a continuous worldwide basis. The accuracy of this service will be established by the DOD and DOT based on U. S. security interests. SPS provides a predictable positioning accuracy of 100 meters (95 percent) horizontally and 156 meters (95 percent) vertically and time transfer accuracy to UTC within 340 nanoseconds (95 percent). Precise Positioning Service : The FRP defines the Precise Positioning Service (PPS) as: the most accurate direct positioning, velocity, and timing information continuously available, worldwide, from the basic GPS. This service is limited to users specifically authorized by the U.S. P(Y)-code capable military user equipment provides a predictable positioning accuracy of at least 22 meters (95 percent) horizontally and 27.7 meters (95 percent) vertically and time transfer accuracy to UTC within 200 nanoseconds (95 percent) (DoD and DoT 1995, A-36). By the time the 1992 FRP was published, the projected 1995 estimate of 53,000 civil users of GPS exceeded the projected number of military users estimated at 19,000 (U.S. DoD and DoT 1993, 3-41). Civil users now constitute the majority of GPS users. The 1994 FRP estimates the current total number of GPS users at over 500,000 in the United States alone (U. S. DoD and DoT 1995, 3-7).
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GPS Segments : The Global positioning System (GPS) comprises three segments : The space segment (all function satellites) The Control segment (all ground station involved in the monitoring of the system: master control station, monitoring stations & ground control) The user segment (all civil and military GPS users)
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Space Segment : The Space Segment is designed to consist of 24 satellites orbiting the earth at approximately 20200Km every 12 hours. At time of writing there are 26 operational satellites orbiting the earth. The space segment is so designed that there will be a minimum of 2 to 3 satellite visible above a 15deg cut off angle at any point of the earth's surface at anyone time. Each GPS satellite has several very accurate atomic clocks on board. The clocks operate at a fundamental frequency of 10.23MHz. This is used to generate the signals that are broadcast from the satellite.
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Figure 2
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Hi Position of the 28 GPS satellites at 12.00 hrs UTC on 14th April 2001 Figure 3 Control Segment : The Control Segment consists of one master control station, 5 monitor stations and 4 ground antennas distributed among 5 locations roughly on the earth equator. The Control Segment tracks the GPS satellites, updates their orbiting position and calibrates and synchronizes their clocks. A further important function is to determine the orbit of each satellite and predict its path for the following 24 hours. This information is uploaded to each satellite and subsequently broadcast from it. This enables the GPS receiver to know where each satellite can be expected to be found. The satellite signals are read at Ascension, Diego, Garcia & Kwajalein. The measurements are then sent to the master control station in Colorado Springs where they are processed to determine any errors in each satellite. The information is then sent back to the four monitoring stations equipped with ground antennas and uploaded to the satellites. Scientech Technologies Pvt. Ltd.
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Figure 4 User Segment : The User Segment comprises of anyone using a GPS receiver to receive the GPS signal and determine their position and / or time. Typical applications within the user segment are land navigation for hikers, vehicle location, surveying, marine, navigation, aerial navigation, machine control etc.
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Figure 6 a Scientech Technologies Pvt. Ltd.
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Figure 6 b Information Transmitted by the satellites? The following is the key information transmitted by the satellites constellation on either a continuous or periodical basis. 1.
Satellite Health
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Ephemeredes
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Constellation Almanac
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Time
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Ranging Signals
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Atmospheric Correctional Data
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The Ephemeredes describe the detailed orbital characteristics of the satellite from which it is transmitted. Simply this is the satellite's mechanism for describing where it is.
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The satellites Almanac describe the course orbital data for all satellites in the constellation. Simply this data describes where all the satellites are, roughly, allowing the receiver to know where to look, roughly, for a satellite.
Satellites are identified by : 1.
Space Vehicle Number (SVN), and
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Pseudo Random Noise number (PRN)
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This data is broadcast to the User Segment so that it can be stored and employed for initial satellite acquisition and for visibility prediction.
The Space Vehic1e number indicates the chronological order in which the satellites were launched. Most GPS Receivers employ the PRN to identify which satellite they are observing. How does it Work? Some Principles to Acknowledge There are 24 operational satellites They orbit the earth approximately every 12 hours They are positioned in six (6) orbital planes Therefore there will usually be something in the order of 6 to 8 satellites visible above the horizon at any point in the world and at any time of the day.
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1.
Each satellite emits information relating to its position, relative to the earth and timing information. This timing information is derived from extremely accurate atomic clocks (cesium or rubidium) that are synchronized to all other satellite clocks and to the ground control stations.
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GPS Receivers are equipped with quartz clocks that are synchronized to GPS time via the data transmitted from the constellation.
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Timing is the basis of location computation.
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The satellite radiates coded signals that are received by the user’s GPS receiver.
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The computation in it simplest form is triangulation. Space Based Triangulation.
Producing Locations : The determination of position is a simple as the following : A signal is transmitted from a satellite containing the Time of Departure of the signal.
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The signal is received by the GPS Receiver and the Time of Arrival is registered.
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We know that Radio waves (the signal) travel at the Speed of Light.
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We know where the satellite is from the information radiated from the satellite.
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Therefore, we can determine the distance from our receiver to a particular satellite. This allows the construction of a hemisphere, whose centre is the satellite and whose radius is the calculated distance from a particular satellite to our receiver.
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When this process is repeated for another satellite that is in view, then the two hemispheres with cut through each other. Repeating this process again with a third satellite and the intersection of the three hemispheres will form a point, which is where your receiver is located. This all seems a bit top heavy, but remember that the satellites are constantly transmitting information and the receiver is usually capable of producing a location result up to 10 times every second. The accepted rule for most receivers is that the receiver must continuously track a minimum of four (4) satellites to produce a location that contains a latitude, longitude and altitude. Of course most receivers available today will track many more satellites than four (4). This is important, as mentioned previously, the constellation operates on 12 hour orbits, therefore the constellation that is visible (being used by the receiver) is always changing, and hence the receiver needs to be looking for new satellites as the current in use satellites begin to disappear from view. Conclusion :
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Experiment 2 Objectives : 1. Understanding the principle of GPS Satellite. 2.
Understanding the generation of L1 carrier frequency.
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Understanding the operation of GPS Receiver.
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Establishing the link between the GPS Satellite and GPS Trainer.
Theory : GPS Satellite Block diagram : On board the Satellite have four atomic clocks. The following time pulses and frequencies required for day-to-day operation are derived from the resonant frequency of one of the atomic clocks shown in figure : The 50Hz data pulse.
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The C/A code pulse (Coarse/Acquisition code, PRN-Code, coarse reception code at a frequency of 1023 MHz), which modulates the data using an exclusive or operation (this spreads the data over a 1 MHz bandwidth).
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The frequency of the civil L1 carrier (1575.42MHz)
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The data modulated by the C/A code modulates the L1 carrier in turn by using Bi-Phase-Shift-Keying (BPSK). With every change in the modulated data there is a 180 deg change in the L1 carrier phase.
Figure 7
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Figure 8 Receiver Block diagram :
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This is the simplest technique employed by GPS receivers to instantaneously give a position and height and / or accurate time to a user. The accuracy obtained is a better than 100m (usually around the 30-50m mark) for civilian users and 5-15m for military users. Procedure of the Experiment : Procedure : Following steps has to be perform while doing the experiments. Step 1 : Please go through the manual before performing any practical. Step 2 : Install the software from the CD ie. Open WinZip from the CD and run the setup file. If you don't have WinZip then please install WinZip from the CD itself. Step 3 : Connect mains cord to the trainer ST2276. Don’t switch on the system now. Step 4 : Connect serial cable to the port which is available on the trainer connect another end of the cable to PC serial port (COM 1, COM 2, COM3 etc.).
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Step 5 : Connect the patch. Antenna to SMA (subminiature) connector of the ST2276 trainer. Step 6 : Place the antenna in the open space ie. Place the antenna outside the window. Step 7 : Switch on the trainer ST2276. Step 8 : Precaution, don't touch the antenna during the on condition. Step 9 : Open software from start / program file IGPS Diag. Now click on option like COM1, if it is not possible to detect then check your PC com port. If your PC com port is COM2 then click COM2 in the software. As soon as you click on any of these com port according to your PC the software will start displaying some signals. After this click on stop button, below I have shown you the software window.
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Hi Figure 10 Step 10 : Here in the above software window we have not mention any reading, actually this experiment is only to study the GPS SV, L1 and GPS receiver. But in your case you will get some readings but don't take at present just see. In the next experiments you have to analysis all this reading. Conclusion :
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Experiment 3 Objective : 1. Understanding the shape of Earth. 2.
Measurement of latitude, longitude.
Theory : Earth Shape : A significant problem when using the GPS system is that there are very many coordinate systems worldwide. As a result, the position measured an calculated by the GPS system does not always coincide with one's supposed position. In order to understand how the GPS system functions, it is necessary to take a look at the basics of the science that deals with the surveying and mapping of the Earth surface, geodesy. Without this basic knowledge, it is difficult to understand why with a good portable GPS receiver the right combination has to be selected from more than 100 different map reference systems. If an incorrect choice is made, a position can be out by several hundred meters.
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Different Earth Shapes like : Geoids
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Spheroid
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Worldwide reference ellipsoid WGS-84
Format of latitudes and longitudes :
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Where a numeric latitude or longitude is given, the two digits immediately to the left of the decimal point are whole minutes, to the right are decimals of minutes, and the remaining digits to the left of the whole minutes are whole degrees. Eg. 4533.35 is 45 degrees and 33.35 minutes. ".35" of a minute is exactly 21 seconds. Eg. 16708.033 is 167 degrees and 8.033 minutes. “.033” of a minute is about 2 seconds. Procedure : Following steps has to be perform while doing the experiments. Step 1 : Please go through the manual before performing any practical. Step 2 : Install the software from the CD ie. Open WinZip from the CD and run the setup file. If you don't have WinZip then please install WinZip from the CD itself. Step 3 : Connect mains cord to the trainer ST2276. Don't switch on the system now. Step 4 : Connect serial cable to the port which is available on the trainer. Connect another end of the cable to PC serial port (COM1, COM2, COM3 etc.). Step 5 : Connect the patch antenna to SMA (subminiature) connector of the ST2276 trainer. Step 6 : Place the antenna in the open space ie. Place the antenna outside the window. Scientech Technologies Pvt. Ltd.
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Step 7 : Switch on the trainer ST2276. Step 8 : Precaution, don't touch the Step 9 : Open software from start / program file /GPS Diag. Now click on option like COM1, if it is not possible to detect then check your PC com port. If your PC com port is COM2 then click COM2 in the software. As soon as you click on any of these com port according to your PC the software will start displaying some signals. After this click on stop button, now go to the observation table for noting down the values. Step 10 : Take at least four reading by placing the antenna at four different locations. But switch off the power during placing the antenna on different location. Sample observation taken during testing : Latitude
Longitude
Longitude
Country
City
State
Country
Result & Conclusion :
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Latitude
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Observation :
City
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Experiment 4 Objective : 1. Understanding the principle of PRN code in GPS. 2.
Understanding the principal of autocorrelation in GPS.
Theory : PRN codes : This section describes the principle of the PRN code that is used and its use for GPS. PRN stands for Pseudo Random Noise. In normal language it means consists of a long series of bits (0’s and 1’s). At first sight there doesn’t seem to be a regular pattern in the bits. But there is! The codes-patterns used for GPS repeat themselves after the 1023rd bit. These codes can be easily made with very few digital elements. For the 1023 bit pattern 10 shifting registers and some digital adders are needed. In general with n shifting registers a series of 2n -1 bits can be generated. For n = 10 this will become 1024 (= 210) - 1 = 1023 bits. The codes are generated with a speed of 1.023 MHz (or 1023000 bits per second). An example with four shifting elements is given in the picture below.
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The GPS satellites broadcast the PRN codes mixed (see picture below) with the other GPS information, like orbital (also called ephemeris) and clock-parameters, but also parameters concerning the other satellites. By mixing the PRN-code with the 50 Hz data the total signal is spread out over a broad part of the spectrum. This technique is called spread spectrum. This section won't go very deep in this complex matter, but the result is that the signal power is very low, even beneath the noise floor. In other words: it has become very hard to distinguish the signal from noise (that is always present on signals).
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Figure 11
Figure 12 When the GPS signals are received by the user of GPS, the PRN-code and GPS data have to be separated. This is done by again mixing the received signal with a locally generated PRN-code. This must be the same PRN-code which has been generated in the satellite. It is important that equal parts of the code are mixed with each other. Therefore the code generated in the receiver must be shifted in time until the two codes are exactly synchronous. In this special case when the receiver ‘locks’ (also
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referred as full correlation) the two codes can block .each other out and the GPS-data remains and can be further processed. This method is called dispreading.
Figure 13
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Every satellite has its own unique PRN-code so that the GPS receiver can distinguish the signals from various satellites. GPS receiver is able to generate 32 PRN-codes. Until now so many satellites have not been launched.
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When the GPS receiver has to start up it doesn't know which GPS signal is from which satellite. Therefore it tries to lock with the 32 known PRN-codes one by one. If one code locks then the information of one satellite can be decoded. This information also contains data about other satellites and the rest can soon be received too. The main reason for using PRN codes in the GPS system is that the PRN code enlarges the unambiguous measurement range. One must keep in mind that after 1023 bits the code is repeated. It is case that GPS-receiver is aware it is ‘looking’ at the right code and not at its predecessor or successor. Looking at the wrong code gives a navigation error of 300 km (corresponding to the code length of 1 millisecond). Autocorrelation : The ideal GPS receiver would have an infinitely wide receiver BW which would allow the receiver to capture 100% of the GPS spread spectrum signal. The normalized autocorrelation function for an infinitely wide BW is generally illustrated as shown in figure below.
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Theoretical Normalized Auto-correlation Function Figure 14 The auto-correlation peak is maintained by continually adjusting the locally generated code for peak correlator output. The unlimited BW provides a sharp correlation peak and steep early/later slope which facilitates accurate error correction for the codelock-loop (also called Delay Lock Loop).
Conclusion :
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In reality, a GPS receiver would need a brick wall band pass filter with a BW of at least ten times the code C/A code chipping rate to be capable of capturing> 99% of the GPS spread spectrum signal. For most GPS receiver this is generally not practical to achieve.
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Experiment 5 Objective : 1. Understanding the principle of Geometry of the Satellite. 2.
Understanding the importance of PDOP, HDOP, and VDOP.
Theory : DOP (Dilution of Precision) : The accuracy with which a position can be determined using GPS in navigation mode depends, on the one hand, on the accuracy of the individual pseudo-range measurements and on the other, on the geometrical configuration of the satellites used. This is expressed in a quality, which in navigation literature is termed DOP (Dilution of Precision). There are several DOP designations in current use : GDOP : Geometrical DOP (position in 3-D space, incl. time deviation in the solution). PDOP : Position DOP (position in 3-D).
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HDOP : Horizontal DOP (position on a plane).
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VDOP : Vertical DOP (height only).
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The accuracy of any measurement is proportionately dependent on the DOP value. This means that if the DOP value doubles the error in determining a position increases by a factor of two.
Figure 15 Satellite Geometry and PDOP : PDOP can be interpreted as a reciprocal value of the volume of a tetrahedron, formed by the positions of the satellites and user, as shown in figure. The best geometrical situation occurs when the volume is at a maximum and PDOP at minimum. PDOP played an important part in the planning of measurement projects during the early year of GPS, as the limited deployment of satellites frequently produced phases when satellite constellations were geometrically very unfavorable. Satellite deployment today is so good that PDOP and GDOP values rarely exceed 3. Scientech Technologies Pvt. Ltd.
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It is therefore unnecessary to plan measurements based on PDOP values, or to evaluate the degree of accuracy attainable as a result, particularly as different PDOP values can arise over the course of a few minutes. In the case of kinematic applications and rapid recording processes, unfavorable geometrical situation that are short lived in nature can occur in isolated case. The relevant PDOP values should therefore be included as evaluation criteria when assessing critical results. PDOP values can be shown with all planning and evaluation programmes supplied by us in figure below.
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HDOP = 2, 2 DOP = 6, 4 PDOP = 6, 8
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Following steps has to be perform while doing the experiments.
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Step 1 : Please go through the manual before performing any practical. Step 2 : Install the software from the CD i.e. Open WinZip from the CD and run the setup file. If you don't have WinZip then please install WinZip from the CD itself. Step 3 : Connect mains cord to the trainer ST2276. Don't switch on the system now. Step 4 : Connect serial cable to the port which is available on the trainer connect another end of the cable to PC serial port (COM1, COM2, COM3 etc.). Step 5 : Connect the patch antenna to SMA (subminiature) connector of the ST2276 trainer. Step 6 : Place the antenna in the open space i.e. Place the antenna outside the window. Step 7 : Switch on the trainer ST2276 Step 8 : Precaution, don’t touch the antenna during the on condition. Step 9 : Open software from start/program file / GPS diag. Now click on option like COM 1, if it is not possible to detect then check your PC COM1, if it is not possible to detect then check your PC com port. If your PC com port is COM2 then click COM2 in the software. As soon as you click on any of these com port according to
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your PC the software will start displaying some signals. After this click on stop button, now go to the observation table for noting down the values. Step 10 : Take at least four reading by placing the antenna at four different locations. But switch off the power during placing the antenna on different location.
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Sample observation taken during testing :
Figure 17
PDOP
HDOP
VDOP
Observation : PDOP
HDOP
VDOP
Result & Conclusion :
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Experiment 6 Objective : 1. Understanding the principle of NMEA 0183 protocol 2.
Analysis of NMEA 0183 protocols
Theory : Common NMEA Sentence : NMEA stands for National Marine Electronic Association. NMEA is a standard protocol; use By GPS receivers to transmit data. NMEA output is EIA-422A but for most purposes you can consider it RS-232 compatible. Use 4800 bps, 8 bits, no parity and one stop bit (8N1). NMEA 0183 sentences are all ASCII. Each sentence begins with a dollarsign ($) and ends with a carriage return linefeed (
). Data is comma delimited. All commas must be included as they act as markers. Some GPS do not send some of the fields. A checksum is optionally added (in a few cases it is minatory). Following the $ is the address field aaccc. aa is the device id. GP is used to identify GPS data. Transmission of the device ID is usually optional ccc is the sentence formatter, otherwise known as the sentence name.
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RMC
$GPRMC, hhmmss.ss,A,llll.ll,a,yyyyy.yy,a,x.x,x.x,ddmmyy,x.x,a*hh
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RMC = Recommended Minimum Specific GPS/TRANSIT Data
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1 = UTC of position fix 3 = Latitude of fix 4 = N or S 5 = Longitude of fix
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2 = Data status (V = navigation receiver warning)
6 = E or W 7 = Speed over ground in knots 8 = Track made good in degrees True 9 = UT date 10 = Magnetic variation degrees (Easterly var, subtracts from true course) 11 = E or W 12 = Checksum GGA $GPGGA,hhmmss.ss,llll.ll,a,yyyyy.yy,a,x,xx,x.x,x.x,M,x.x,M,x.x,xxxx*hh GGA = Global Positioning System Fix Data 1 = UTC of Position
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2 = Latitude 3 = N or S 4 = Longitude 5 = E or W 6 = GPS quality indicator (0 = invalid; 1 = GPS fix; 2 = Diff. GPS fix) 7 = Number of satellites in use [not those in view] 8 = Horizontal dilution of position 9 = Antenna altitude above/below mean sea level (geoid) 10 = Meters (Antenna height unit) 11 = Geoidal separation (Diff. between WGS-84 earth ellipsoid and mean sea level. = geoid is below WGS-84 ellipsoid) 12 = Meters (Units of geoidal separation) 13 = Age in seconds since last update from diff. reference station
$GPVTG, t,T,,, s.ss, N, s.ss, K*hh
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14 = Diff. reference station ID#
VTG = Actual track made good and speed over ground
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1 = Track made good
2 = Fixed text 'T' indicates that track made good is relative to true north 3 = not used 4 = not used 5 = Speed over ground in knots 6 = Fixed text 'N' indicates that speed over ground in knots 7 = Speed over ground in kilometers/hour 8 = Fixed text 'K' indicates that speed over ground is in kilometers/hour 9 = Checksum GSA $GPGSA,A,3,19,28,14,18,27,22,31,39,,,,,,1.7,1.0,1.3 *35 GSA = GPS receiver operating mode, SVs used for navigation, and DOP values. 1 = Mode : M = Manual, forced to operate in 2D or 3D A = Automatic, 3D/2D Scientech Technologies Pvt. Ltd.
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2 = Mode : 1 = Fix not available 2 = 2D 3 = 3D 3-14 = IDs of SVs used in position fix (null for unused fields) 15 = PDOP 16 = HDOP 17 = VDOP GSV $GPGSV,4,1,13,02,02,213,,03,3,000,,11,00,121,,14,13,172,05*67 GSV = Number of SVs in view, PRN numbers, elevation, azimuth & SNR values. 1 = Total number of messages of this type in this cycle 2 = Message number
Hi
3 = Total number of SV s in view
Co
K-
4 = SV PRN number
5 = Elevation in degrees, 90 maximum
ns
6 = Azimuth, degrees from true north, 000 to 359
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7 = SNR, 00-99 dB (null when not tracking)
8-11 = Information about second SV, same as field 4-7
ing
12-15= Information about third SV, same as field 4-7
16-19= Information about fourth SV, same as field 4-7 Procedure : Following steps has to be perform while doing the experiments. Step 1 : Please go through the manual before performing any practical. Step 2 : Install the software from the CD ie. Open WinZip from the CD and run the setup file. If you don't have WinZip then please install WinZip from the CD itself. Step 3 : Connect mains cord to the trainer ST2276. Don't switch on the system now. Step 4 : Connect serial cable to the port which is available on the trainer. Connect another end of the cable to PC serial port (COM1, COM2, COM3 etc.). Step 5 : Connect the patch antenna to SMA (subminiature) connector of the ST2276 trainer. Step 6 : Place the antenna in the open space ie. Place the antenna outside the window. Step 7 : Switch on the trainer ST2276.
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Step 8 : Precaution, don't touch the antenna during the on condition. Step 9 : Open software from start/program file /GPS Diag. Now click on option like COM1, if it is not possible to detect then check your PC com port. If your PC com port is COM2 then click COM2 in the software. As soon as you click on any of these com port according to your PC the software will start displaying some signals. After this click on stop button, now go to the observation table for noting down the values. Step 10 : In the observation you have to map the above theory with the actual realtime readings. Sample Observation taken during testing :
Hi Co
K-
Note :
Figure 18
This is the sample observation, in your case you have a map received data reading with the above theory, it’s very interesting.
$GPGLL
ing
$GPGGA
ult
$GPVTG
ns
Observation :
$GPGSA $GPGSV $GPRMC $GPVTG Result & Conclusion :
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Experiment 7 Objective : Study of other NMEA Sentence Theory : GPS - NMEA sentence information All $GPxxx sentence codes and short descriptions $GPAAM - Waypoint Arrival Alarm $GPALM – GPS Almanac Data $GPAPA – Autopilot format “A” $GPAPB – Autopilot format “B” $GPASD – Autopilot System Data $GPBEC - Bearing Distance to Waypoint, Dead Reckoning $GPBOD - Bearing, Origin to Destination
Hi
$GPBWC - Bearing & Distance to Waypoint, Great Circle
K-
$GPBWR - Bearing & Distance to Waypoint, Rhumb Line
Co
$GPBWW - Bearing, Waypoint to Waypoint $GPDBT - Depth Below Transduce $GPDPT - Depth $GPFSI - Frequency Set Information
ing
ult
ns
$GPDCN - Decca Position
$GPGGA - Global Positioning System Fix Data $GPGLC - Geographic Position, Loran-C
$GPGLL - Geographic Position, Latitude/Longitude $GPGRS - GPS Range Residuals $GPGSA - GPS DOP and Active Satellites $GPGST - GPS Pseudorange Noise Statistics $GPGSV - GPS Satellites in View $GPGXA - TRANSIT Position $GPHDG - Heading, Deviation & Variation $GPHDT - Heading, True $GPHSC - Heading Steering Command $GPLCD - Loran-C Signal Data $GPMSK - Control for a Beacon Receiver Scientech Technologies Pvt. Ltd.
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$GPMSS - Beacon Receiver Status $GPMTA - Air Temperature (to be phased out) $GPMTW – Water Temperature $GPMWD Wind Direction $GPMWV – Wind Speed and Angle $GPOLN – Omega Lane Numbers $GPOSD - Own Ship Data $GPR00 - Waypoint active route (not standard) $GPRMA - Recommended Minimum Specific Loran-C Data $GPRMB - Recommended Minimum Navigation Information $GPRMC - Recommended Minimum Specific GPS/TRANSIT Da $GPROT - Rate of Turn $GPRPM - Revolutions
Hi
$GPRSA - Rudder Sensor Angle
K-
$GPRSD - RADAR System Data
Co
$GPRTE - Routes
$GPTRF - Transit Fix Data $GPTTM - Tracked Target Message
ing
ult
$GPSTN - Multiple Data I
ns
$GPSFI - Scanning Frequency Information
$GPVBW - Dual Ground/Water Speed $GPVDR - Set and Drift $GPVHW - Water Speed and Heading $GPVLW - Distance Traveled through the water $GPVPW- Speed, Measured Parallel to Wind $GPVTG - Track Made Good and Ground Speed $GPWCW - Waypoint Closure Velocity $GPWNC - Distance, Waypoint to Waypoint $GPWPL - Waypoint Location $GPXDR - Transducer Measurement $GPXTE - Cross-Track Error, Measured $GPXTR - Cross-Track Error, Dead Reckoning
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$GPZDA - UTC Date / Time and Local Time Zone Offset $GPZFO - UTC & Time from Origin Waypoint $GPZTG - UTC & Time to Destination Waypoint 26 interpreted sentences transmitted by GPS unit : $GPAAM - Waypoint Arrival Alarm $GPALM - GPS Almanac Data (Can also be received by GPS unit) $GPAPB - Autopilot format "B" $GPBOD - Bearing, origin to destination $GPBWC - Bearing and distance to waypoint, great circle $GPGGA - Global Positioning System Fix Data $GPGLL - Geographic position, latitude /longitude $GPGRS - GPS Range Residuals $GPGSA - GPS DOP and active satellites
Hi
$GPGST - GPS Pseudorange Noise Statistics
K-
$GPGSV - GPS Satellites in view
Co
$GPHDT - Heading, True
ult
$GPMSS - Beacon Receiver Status
ns
$GPMSK - Control for a Beacon Receiver
$GPR00 - List of waypoints in currently active route
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$GPRMA - Recommended minimum specific Loarn-C data $GPRMA - Recommended minimum navigation info $GPRMC - Recommended minimum specific GPS/Transit data $GPRTE - Routes $GPTRF - Transit Fix Data $GPSTN - Multiple Data ID $GPVBW - Dual Ground / Water Speed $GPVTG - Track made good and ground speed $GPWPL - Waypoint location $GPXTE - Cross-track error, measured $GPZDA - UTC Date / Time and Local Time Zone Offset
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$GPAAM : Waypoint Arrival Alarm This sentence is generated by some units to indicate the Status of arrival (entering the arrival circle, or passing the perpendicular of the course line) at the destination waypoint. $GPAAM, A, A, 0.10, N, WPTNME*43 Where: AAM Arrival Alarm A Arrival circle entered A Perpendicular passed 0.10 Circle radius N Nautical miles WPTNME Waypoint name
Co
GPS Almanac Data
K-
$GPALM :
Hi
*43 Checksum data
ult
ns
A set of sentences transmitted by some Garmin units in response to a received $PGRMO, GPALM, 1 sentence. It can also be received by some GPS units (eg. Garmin GPS 16 and GPS 17) to initialize the stored almanac information in the unit. 1 = Total number of sentences in set
ing
Example 1: $GPALM,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,*CC 2 = Sentence sequence number in set 3 = Satellite number 4 = GPS week number 5 = Bits 17 to 24 of almanac page indicating SV health 6 = Eccentricity 7 = Reference time of almanac 8 = Inclination angle 9 = Right ascension rate 10 = Semi major axis route 11 = Argument of perigee (omega) 12 = Ascension node longitude 13 = Mean anomaly
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14 = af0 clock parameter 15 = af1 clock parameter Example : $GPALM,1,1,15,1159,00,441d,4e,16be,fd5e,a10c9f,4a2da4,686e81,58cbe1,0a4,001 *5B Field Example Comments Sentence ID
$GPALM
Number of messages
1
Total number of message in sequence
Sequence number
1
Satellite PRN
15
This is first message in sequence Unique ID (PRN) of satellite message relates to
GPS week number
1159
SV health
00
Eccentricity
441d
Reference time
4e
Almanac reference time
Hi
16be
Rate of right ascension
K-
Inclination angle
Bits 17-24 of almanac page
Roor of semi-major axis
a10c9f
Argument of perigee
4a2da4
Longitude of ascension node
686e81
Mean anomaly
58 cbe 1
ing
F0 clock parameter
ult
ns
Co
Fd5e
F1 clock parameter Checksum
*5B
$GPAPB : Autopilot format "B" This sentence is sent by some GPS receivers to allow them to be used to control an autopilot unit. This sentence is commonly used by autopilots and contains navigation receiver warning flag status, cross-track-error, waypoint arrival status, initial bearing from origin waypoint to the destination, continuous bearing from present position to destination and recommended heading-to-steer to destination waypoint for the active navigation leg of the Journey.
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Note : Some autopilots, Robertson in particular, misinterpret "bearing from origin to destination" as "bearing from present position to destination". This is likely due to the difference between the APB sentence and the APA sentence, for the APA sentence this would be the correct thing to do for the data in the same field. AP A only differs from APB in this one field and APA leaves off the last two fields where this distinction is clearly spelled out. This will result in poor performance if the boat is sufficiently off-course that the two bearings are different. $GPAPB, A, A, 0.10, R, N, V, V, 011, M, DEST, 011, M, 011, M*82 where : APB Autopilot format B A Loran-C blink/SNR warning, general warning A Loran-C cycle warning 0.10 cross-track error distance R steer Right to correct (or L for Left)
ns
V arrival alarm - perpendicular
Co
V arrival alarm - circle
K-
Miles (K for kilometers)
Hi
N cross-track error units - nautical
011, M magnetic bearing, origin to destination
ing
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DEST destination waypoint ID
011, M magnetic bearing, present position to destination 011, M magnetic heading to steer (bearings could True as 033, T) $GPBOD : Bearing Origin to Destination Eg. BOD, 045. T, 023. M, DEST, START 045., T bearing 045 degrees True from "START" to "DEST" 023., M beraing 023 degrees Magnetic from “START” to “DEST” "DEST" destination waypoint ID START origin waypoint ID Example 1: $GPBOD, 099.3, T, 105.6, M, POINTB,*01 Waypoint ID: "POINTB" Bearing 99.3 True, 105.6 Magnetic. This sentence is transmitted in the GOTO mode, without an active route on your GPS.
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Warning : this is the bearing from the moment you press enter in the GOTO page to the destination waypoint and is NOT updated dynamically! To update the information, (current bearing to waypoint), you will have to press enter in the GOTO page again. Example 2 : $GPBOD,097.0,T,103.2,M,POINTB,POINTA*52 This sentence is transmitted when a route is active. It contains the active leg information: origin waypoint "POINTA" and destination waypoint "POINTB", bearing between the two points 97.0 True, 103.2 Magnetic. It does NOT display the bearing from current location to destination waypoint! WARNING Again this information does not change until you are on the next leg of the route. (The bearing from POINTA to POINTB does not change during the time you are on this leg.) $GPBWC : Bearing and distance to waypoint, great circle Eg 1. $GPBWC, 081837,,,,,, T,,M,,N,*13 BWC, 225444,4917.24,N,12309.57,W, 051.9,T,031.6,M,001.3,N,004*29
Hi
225444 UTC time of fix 22:54:44
K-
4917.24, N Latitude of waypoint
Co
12309.57, W Longitude of way point
ns
051.9, T Bearing to waypoint, degrees true
031.6, M Bearing to waypoint, degrees magnetic
ult
001.3, N Distance to waypoint, Nautical miles
ing
004 Way point ID
Eg 2. $GPBWC, 220516,5130.02, N,00046.34,W,213.8,T,218.0,M,0004.6,N,EGL M*11 1 2 3 4 5 6 7 8 9 10 11 12 13 1.
220516 timestamp
2.
5130.02 Latitude of next waypoint
3.
N North/South
4.
00046.34 Longitude of next waypoint
5.
W East/West
6.
213.0 True track to waypoint
7.
T True Track
8.
218.0 Magnetic track to waypoint
9.
M Magnetic.
10.
0004.6 range to waypoint
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11.
N unit of range to waypoint, N = Nautical miles
12.
EGLM Waypoint name
13.
11 checksum
$GPGGA : Global Positioning System Fix Data Eg l., $GPGGA, 170834, 4124.8963,N,08151.6838,W,1,05,1.5,280.2,M 34.0,M,,, *75 Name
Example Data
Description
Sentence Identifier
$GPGGA
Global Positioning System Fix Data
Time
170834
17:08:34 UTC
Latitude
4124.8963N
41d24.8963’N or 41d 24’54” N
Longitude
08151.6838,W
81d 51.6838’ W or 81d 51’41” W
Fix Quality : -0 = Invaild – 1 = GPs fix 2 = DGPS fix
1
Data is from a GPS fix
05
Hi
5 Satellites are in view
Horizontal Dilution of precision (HDOP)
K-
Relative accuracy of horizontal position
Altitude Height of geoid above WGS84 ellipsoid
280.2,M
280.2 meters above mean sea level
Time since last DGPS update
Blank
DGPS reference station id
Blank
Checksum
*75
Number of Satellites
1.5
ns
Co
-34.0 M
-34.0 meters
ing
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No last update No station id
Used by program to check for transmission errors
Global Positioning System Fix Data. Time, position and fix related data for a GPS receiver. Eg2.$PGGA,hhmmss.ss,ddmm.mmm,a,dddmm.mmm,b,q,xx,p.p,a.b,M,c.d,M,x.x, nnnn hhmmss.ss = UTC of position ddmm.mmm = latitude of position a = N or S, latitutde hemisphere dddmm.mmm = longitude of position b = E or W, longitude hemisphere q = GPS Quality indicator (0 = No fix, 1 = Non-differential GPS fix, Scientech Technologies Pvt. Ltd.
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2 = Differential GPS fix, 6 = Estimated fix) xx = number of satellites in use p.p = horizontal dilution of precision a.b = Antenna altitude above mean-sea-level M = units of antenna altitude, meters c.d = Geoidal height M = units of geoidal height, meters x.x = Age of Differential GPS data (seconds since last valid RTCM transmission) nnnn = Differential reference station ID, 0000 to 1023 $GPGLL : Geographic Position, Latitude / Longitude and time. eg1. $GPGLL, 3751.65, S, 14507.36, E*77 eg2. $GPGLL, 4916.45, N, 12311.12, W, 225444, A
Hi
4916.46, N Latitude 49 deg. 16.45 min. North
K-
12311.12, W Longitude 123 deg. 11.12 min. West
ns
A Data Valid
Co
225444 Fix taken at 22:54:44 UTC
12345 5133.81 Current latitude
2.
N North/South
3.
00042.25 Current longitude
4.
W East/West
5.
*75 checksum
ing
1.
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Eg 3. $GPGLL, 5133.81, N, 00042.25, W*75
$--GLL,lll.ll,a,yyyyy.yy,a,hhmmss.ss,A llll.ll = Latitude of position a = N or S yyyyy.yy = Longitude of position a = E or W hhmmss.ss = UTC of position A = status : A = valid data
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$GPGRS : GPS Range Residuals Example : $GPGRS, 024603.00, 1,-1.8, -2.7, 0.3,,,,,,*6C Field
Example
Comment
Sentence ID
$GPGRS
UTC Time
024603.00
UTC time of associated GGA fix
Mode
1
0 = Residuals used in GGA, 1 = residuals calculated after GGA
Sat 1 residual
- 1.8
Residual (meters) of satellite 1 in solution
Sat 2 residual
- 2.7
The order matches the PRN numbers in the GSA sentence
Sat 3 residual
0.3
Sat 4 residual
Unused entries are blank
Sat 5 residual Sat 7 residual Sat 9 residual
Sat 12 residual
ing
ult
Sat 11 residual
ns
Sat 10 residual
Co
K-
Sat 8 residual
Hi
Sat 6 residual
Checksum *6C $GPGSA : GPS DOP and active satellites Eg 1. $GPGSA, A, 3, 16, 18, 24, 3.6, 2.1, 2.2*3C Eg2. $GPGSA, A, 3, 19, 28,14,18,27, 22, 31, 39, 1.7, 1.0, 1.3*34 1 = Mode : M = Manual, forced to operate in 2D or 3D A=Automatic, 3D/2D 2= Mode : 1 = Fix not available 2 = 2D 3 = 3D 3 - 14 = PRN's of Satellite Vehicles (SV's) used in position fix (null for unused fields) 15 = Position Dilution of Precision (PDOP) 16 = Horizontal Dilution of Precision (HDOP) 17 = Vertical Dilution of Precision (VDOP) Scientech Technologies Pvt. Ltd.
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$GPGST : GPS Pseudorange Noise Statistics Example: $GPGST, 024603.00, 3.2, 6.6, 4.7, 47, 3, 5.8, 5.6, 22.0*58 Field Example Comments Sentence ID $GPGST UTC Time
024603.00
RMS Deviation
3.2
Semi-major deviation
6.6
Standard deviation of ranges inputs to the navigation solution.
Semi-minor deviation
4.7
Standard deviation (meters) of semi-major axis of error ellipse
Semi-major orientation
47.3
Orientation of semi-major axis of error ellipse (true north degrees)
Latitude error
5.8
Standard deviation (meters) of latitude error
22.0
Checksum
*58
Standard deviation (meters) of latitude error
ult
Altitude error deviation
Standard deviation (meters) of longitude error
ns
5.6
Co
Longitude error deviation
K-
Hi
Deviation
UTC time of associated GGA fix Total RMS standard deviation of ranges inputs to the navigation solution
ing
$GPGSV : GPS Satellites in view Eg. $GPGSV, 3, 1,11,03,03,111,00,04,15, 270, 00, 06, 01, 010, 00, 13, 06, 292, 00*74 $GPGSV,3,2,11,14, 25,170,00,16,57,208,39,18,67,296,40,19,40,246,99*74 $GPGSV, 3, 3,11,22,42, 067, 42, 24, 14, 311 43, 27, 05, 244, 00,,,,*4D $GPGSV,1,1,13,02,02,213,03,-3,000,11,00,121,14,13,172,05*62 1 = Total number of messages of this type in this cycle 2 = Message number 3 = Total number of SVs in view 4 = SV PRN number 5 = Elevation in degrees, 90 maximum 6 = Azimuth, degrees from true north, 000 to 359 7 = SNR, 00-99 dB (null when not tracking) 8-11 = Information about second SV, same as field 4-7 12-15= Information about third SV, same as field 4-7 16-19= Information about fourth SV, same as field 4-7 Scientech Technologies Pvt. Ltd.
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Co
K-
$ GPMSS : Beacon Receiver Status
Hi
$GPHDT : Heading, True. Actual vessel heading in degrees true produced by any device or system producing true heading. $--HDT, x.x,T x.x = Heading, degrees True $GPMSK : Control for a Beacon Receiver $GPMSK, 318.0, A, 100, M, 2*45 where : 318.0 A Frequency to use A Frequency mode, A = auto, M = manual 100 Beacon bit rate M Bitrate, A=auto, M=manual 2 frequency for MSS message status (null for no status) *45 checksum
ns
Example 1: $GPMSS, 55, 27,318.0, 100,*66 Where :
ult
55 signal strength in dB
ing
27 signal to noise ratio in dB 318.0 Beacon Frequency in KHz 100 Beacon bitrate in bps *66 checksum
Example 2 : $GPMSS,0.0,0.0,0.0, 25,2*6D Field
Example
Sentence ID
$GPMSS
Signal strength
0.0
Signal strength (dB 1uV)
SNR
0.0
Signal to noise ratio (dB)
Frequency
0.0
Beacon frequency (KHz)
Data rate
25
Beacon frequency (BPS)
Unknown field
2
Unknown field sent by GPS receiver used for test
Checksum
*6D
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Comments
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$GPR00 : List of waypoint IDs in currently active route Egl. $GPR00, EGLL, EGLM, EGTB, EGUB, EGTK, MBOT, EGTB""",* 58 Eg2.$GPR00,MINST,CHATN,CHAT1,CHATW,CHATM,CHATE,003,004,005,006, 007,,*05 List of waypoints. This alternates with $GPWPL cycle Which itself cycles waypoints. $GPRMA : Recommended minimum specific Loran-C data Eg. $GPRMA,A,lll,N,lll,W,x,y,ss.s,ccc, vv.v,W*hh A = Data status lll = Latitude N = N/S
y = not used ss.s = Speed over ground in knots
W = Direction of variation E/W
ing
vv.v = Variation
ult
ccc = Course over ground
ns
Co
x = not used
K-
S =W/E
Hi
lll = longitude
hh = Checksum $GPRMB : Recommended minimum navigation information (sent by nav. receiver when a destination waypoint is active) eg 1. $GPRMB,A,0.66,L,003,004,4917.24, N, 12309.57, W,001.3,052.5,000.5,V*0B A Data status A = OK, V = warning 0.66, L Cross-track error (nautical miles, 9.9 max.), Steer Left to correct (or R = right) 003 Origin waypoint ID 004 Destination waypoint ID 4917.24, N Destination waypoint latitude 49 deg. 17.24 min. N 12309.57, W Destination waypoint longitude 123 deg. 09.57 min.W
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001.3 Range to destination, nautical miles 052.5 True bearing to destination 000.5 Velocity towards destination, knots V Arrival alarm A = arrived, V = not arrived *0B = mandatory checksum eg 2. $GPRMB,A,4.08,L,EGLL,EGLM, 5130.02,N,00046.34, W,004.6, 213.9,122.9,A*3D 1 2 3 4 5 6 7 8 9 10 11 12 13 A validity
2.
4.08 off track
3.
L Steer Left (L/R)
4.
EGLL last waypoint
5.
EGLM next waypoint
6.
5130.02 Latitude of Next waypoint
7.
N North/South
8.
00046.34 Longitude of next waypoint
9.
W East/West
10.
004.6 Range
11.
213.9 bearing to wept.
12.
122.9 closing velocity
13.
A validly
14.
*3D checksum
ing
ult
ns
Co
K-
Hi
1.
eg3. $GPRMB,A,x.x,a,c--c,d--d,llll.ll,e,yyyyy.yy,f,g.g,h.h,i.i,j *kk 1.= Data Status (V= navigation receiver warning) 2.= Cross track error in nautical miles 3.= Direction to steer (L or R) to correct error 4.= Origin waypoint ID# 5.= Destination waypoint ID# 6.= Destination waypoint latitude 7.= N or S 8.= Destination waypoint longitude
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9.= E or W 10 = Range to destination in nautical miles 11 = Bearing to destination, degrees True 12 = Destination closing velocity in knots 13 = Arrival status; (A = entered or perpendicular passed) 14 = Checksum Recommended minimum specific GPS/Transit data : Eg. 1. $GPRMC,081836,A,3751.65,S,14507.36,E,000.0,360.0,130998,011.3,E*62 Eg. 2. $GPRMC,225446,A,4916.45,N,12311.12,W,000.5,054.7,191194,020.3,E*6 8 225446 Time of fix 22:54:46 UTC A Navigation receiver warning A = Valid position, V = Warning 4916.45, N Latitude 49 deg, 16.45 min. North 12311.12, W Longitude 123 deg. 11.12. min. West
Hi
000.5 Speed over ground, Knots
K-
054.7 Course made good, degrees true
Co
191194 UTC Date of fix, 19 November 1994
ult
*68 mandatory checksum
ns
020.3, E Magnetic variation, 20.3 deg. East
1 2 3 4 5 6 7 8 9 10 11 12
ing
Eg.3.$GPRMC,220516,A,5133.82,N,00042.24,W,173.8,231.8,130694,004.2, W*7 0 1.= 220516 Time Stamp 2.= A validity - A-ok, V-invalid 3.= 5133.82 current Latitude 4.= N North/South 5.= 00042.24 current Longitude 6.= W East/West 7.= 173.8 Speed in knots 8.= 231.8 True course 9.= 130694 Date stamp 10 = 004.2 Variation 11 = W East/West 12 = *70 checksum Scientech Technologies Pvt. Ltd.
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Eg. 4. For NMEA 0183 version 3.00 active the Mode indicator field is added $GPRMC, hhmmss.ss,A,llll.ll,a,yyyyy.yy ,a,x.x,x.x,ddmmyy,x.x,a,m *hh Field # 1.= UTC time of fix 2.= Data status (A Valid position, V=navigation receiver warning) 3.= Latitude of fix 4.= N or S of longitude 5.= Longitude of fix 6.= E or W of longitude 7.= Speed over ground in knots 8.= Track made good in degrees True 9.= UTC date of fix 10 = Magnetic variation degrees (Easterly var. subtracts from true course) 11 = E or W of magnetic variation
Hi
12 = Mode indicator, (A Autonomous, D=Differential, E Estimated, N Data no valid)
ns
Routes
Co
$GPRTE :
K-
13 = Checksum
ult
Eg. $GPRTE,2,1,c,0,PBRCPK,PBRTO,PTELGR,PPLAND,PY AMBU,PPF AIR, PWARRN, PMORTL, PLISMR *73 1 2 3 4 5...
ing
$GPRTE,2,2,c,0,PCRESY,GRYRIE,GCORIO,GWERR,GWESTG,7FED*3 4 1.= Number of sentences in sequence 2.= Sentence number 3.= 'c' = Current active route, 'w' = waypoint list starts with destination waypoint 4.= Name or number of the active route 5.= onwards, Names ofwaypoints in Route $GPTRF : Transit Fix Data Time, date, position, and information related to a TRANSIT Fix. $--TRF, hhmmss.ss,xxxxxx,llll.ll,a,yyyyy.yy,a,.x,x.x,x.x,x.x,xxx hhmmss.ss = UTC of position fix xxxxxx = Date: dd/mm/yy llll.ll,a = Latitude of position fix, N/S
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yyyyy.yy,a = Longitude of position fix, E/W x.x = Elevation angle x.x = Number of iterations x.x = Number of Doppler intervals x.x = Update distance, nautical miles x.x = Satellite ID $GPSTN : Multiple Data ID : This sentence is transmitted before each individual sentence where there is a need for the Listener to determine the exact source of data in the system. Examples might include dual-frequency depthsounding equipment or equipment that integrates data from a number of sources and produces a single output. $--STN,xx xx = Talker ID number, 00 to 99
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Dual Ground/Water Speed
Hi
$GPVBW :
$-- VBW, x.x, x.x, A, x.x, x.x, A
x.x = Longitudinal water speed, knots
x.x = Longitudinal ground speed, knots
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A = Status: Water speed, A = Data valid
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x.x = Transverse water speed, knots
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Water referenced and ground referenced speed data.
x.x = Transverse ground speed, knots A = Status : Ground speed, A = Data valid $GPVTG : Track Made Good and Ground Speed. Eg, l. $GPVTG, 360.0, T, 348.7, M, 000.0, N, 000.0, K*43 Eg 2. $GPVTG, 054. 7, T, 034.4, M, 005.5, N, 01 0.2, K*41 054.7, T True course made good over ground, degrees 034.4, M Magnetic course made good over ground, degrees 005.5, N Ground speed, N = Knots 010.2, K Ground speed, K = Kilometers per hour Eg3. For NMEA 0183 version 3.00 active the Mode indicator field is added at the end $GPVTG, 054.7, T, 034.4, M, 005.5, N, 010.2, K, A*53 A Mode indicator (A Autonomous, D Differential, E Estimated, N Data not valid) Scientech Technologies Pvt. Ltd.
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$GPWPL : Waypoint location Eg 1. $GPWPL, 4917.16, N, 12310.64, W, 003*65 4917.16, N Latitude of waypoint 12310.64, W Longitude of waypoint 003 Way point ID When a route is active, this sentence is sent once for each waypoint in the route, in sequence. When all waypoints have been reported, GPR00 is sent in the next data set. In any group of sentences, only one WPL sentence, or an R00 sentence, will be sent. Eg 2. $GPWPL, 5128.62, N, 00027.58, W, EGLL*59 123456 5128.62 Latitude of nth waypoint on list
2.
N North/South
3.
00027.58 Longitude of nth waypoint
4.
W East/West
5.
EGLL Ident of nth waypoint
6.
*59 checksum
Eg.1 $ GPXTE, A, A, 0.67, L, N A General warning flag V = warning (Loran-C Blink or SNR warning)
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Cross Track Error, Measured
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$GPXTE :
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Hi
1.
A Not used for GPS (Loarn-C cycle lock flag) 0.67 Cross track error distance L Steer left to correct error (or R for right) N Distance units – Nautical miles Eg 2. $ GPXTE, A, A, 4.07, L, N*6D 123456 1.
A validity
2.
A cycle lock
3.
4.07distance off track
4.
L steer left (L/R)
5.
N distance units
6.
*6D checksum
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$GPZDA : UTC Date/Time and Local Time Zone offset Example 1: $GPZDA,hhmmss.ss,xx,xx,xxxx,xx,xx hhmmss.ss = UTC xx = Day, 01 to 31 xx = Month, 01 to 12 xxxx = Year xx = Local zone description, 00 to +/- 13 hours xx = Local zone minutes description (same sign as hours) Example 2: $GPZDA, 024611.08, 25, 03, 2002, 00, 00*6A Field Sentence ID
Example $GPZDA
Comments
UTC Time
024611.08
UTC time
Hi
UTC Day
UTC day (01 to 31)
03
UTC month (01 to 12)
UTC Year
2002
Local zone hours
00
UTC year (4digit format) Offset to local time zone in hours (+/00 to +/-59)
Local zone minutes
00
Checksum
*6A
UTC Month
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25
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Offset to local time zone in minutes (00 to 59)
Conclusion :
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Experiment 8 Objective : Study of the complete GPS Environment Theory : Now no more theory. Up to experiment no. 7 you have studied all the basics of GPS. Now in this experiment we are analyzing the entire GPS system. You have to take all the readings not only the lab but also in the campus, if possible in the city or state or country or in the entire world. Procedure : Following steps has to be perform while doing the experiments. Step 1 : Please go through the manual before performing any practical. Step 2 : Install the software from the CD ie. Open WinZip from the CD and run the setup file. If you don't have WinZip then please install WinZip from the CD itself. Step 3 : Connect mains cord to the trainer ST2276. Don't switch on the system now.
K-
Hi
Step 4 : Connect serial cable to the port which is available on the trainer. Connect another end of the cable to PC serial port (COM1, COM2, COM3 etc.).
Co
Step 5 : Connect the patch antenna to SMA (subminiature) connector of the ST2276 trainer.
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Step 7 : Switch on the trainer ST2276.
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Step 6 : Place the antenna in the open space ie. Place the antenna outside the window.
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Step 8 : Precaution, don't touch the antenna during the on condition. Step 9 : Open software from start / program file/GPS Diag. Now click on option like COM1, if it is not possible to detect then check your PC com port. If your PC com port is COM2 then click COM2 in the software. As soon as you click on any of these com port according to your PC the software will start displaying some signals. After this click on stop button, now go to the observation table for noting down the values. Step 10 : Take at least four reading by placing the antenna at four different locations. But switch off the power during placing the antenna on different different location.
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K-
Hi Co
Observation :
Figure 19
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In this observation table you have to take readings like UTC Time, UTC Date, Sats Used, Latitude, Longitude, Speed, Altitude, Quality, PDOP, HDOP, VDOP, PRN, Elev, Az, SNR, Used?, & also readings from the received data.
ing
At least you have to take three to four readings on different different places. Please use blank sheet for the observation and make at least four columns for four different places. Result & Conclusion :
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1.
2.
3.
4.5 parts in a million
b.
4.5 parts in 100 million
c.
4.5 parts in 10 billion
d.
4.5 parts in a trillion
The following component of the ephemeris error contributes the most to the range error : a.
along-track error
b.
cross-track error
c.
both along-track and cross-track error
d.
radial error
The peak electron density in the ionosphere occurs in a height range of a.
50-100 km
b.
250-400 km
c.
500-700 km
d.
800-1000 km
e.
The refractive index of the gaseous mass in the troposphere is
f.
slightly higher than unity
g.
slightly lower than unity
h.
unity
i.
zero
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5.
a.
Hi
4.
GPS Quiz The relativistic effect in a GPS satellite clock which is compensated by a deliberate clock offset is about :
Rank VDOP, HDOP and PDOP from best to worst (normal conditions): a.
VDOP, HDOP, PDOP
b.
VDOP, PDOP, HDOP
c.
HDOP, VDOP, PDOP
d.
PDOP, HDOP, VDOP
If DGPS corrections to the range measurements are made using the data from a reference station situated at about 100-200 miles, and the resulting position is found to be significantly biased, that means a.
no ionospheric or tropospheric corrections were applied to the measurements at the reference receiver and remote receiver
b.
ionospheric and tropospheric corrections were applied measurements at both the reference receiver and remote receiver
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the
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6.
7.
None of the above
The UTC time and the GPS time are offset by an integer number of seconds (e.g., 13 seconds as of January 1, 2001), as well as a fraction of a second. The fractional part is about : a.
0.1 – 0.5 sec
b.
1-2 ms
c.
100-200 ns
d.
10-20 ns
The differences between pseudorange and carrier phase observations are : a.
Integer ambiguity, multipath errors and receiver noise.
b.
Satellite clock, integer ambiguity, multipath errors and receiver noise.
c.
Integer ambiguity, ionospheric errors, multipath errors and receiver noise.
d.
Satellite clock, integer ambiguity, ionospheric errors, multipath errors and receiver noise
If the range measurements for two simultaneously tracking satellites in a receiver are differenced, then the differenced measurement will be free of :
ns
Co
a.
receiver clock error only
b.
satellite clock error and orbital error only
c.
ionospheric delay error and tropospheric delay error only
d.
ionospheric delay error, tropospheric delay error, satellite clock error and orbital error only
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10.
d.
K-
9.
the observations are wrong as there should not be any bias for whether or not ionospheric and tropospheric corrections are applied to the reference and remote receivers
Hi
8.
c.
Zero baseline test (code) can be performed to estimate : a.
receiver noise and multipath
b.
receiver noise
c.
receiver noise, multipath and atmospheric delay errors
d.
none of the above
The NMEA message $GPGLL has fields for a.
latitude-longitude position
b.
speed and heading
c.
satellite elevation-azimuth-signal strength
d.
all of the above
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11.
12.
13.
a.
midnight of Jan 5-6, 1980
b.
midnight of Jan 5-6, 1995
c.
midnight of Dec 31-Jan 1, 1994-1995
d.
midnight of Dec 31-Jan 1, 1999-2000
The complete set of satellite ephemeris data comes once in every. a.
6 seconds
b.
30 seconds
c.
12.5 minutes
d.
12 seconds
For high accuracy of the carrier phase measurements the most suitable carrier tracking loop will be : a.
PLL with low loop bandwidth
b.
FLL with low loop bandwidth
c.
PLL with high loop bandwidth
d.
FLL with high loop bandwidth
Co
K-
Hi
14.
GPS week number started incrementing from zero at
ns
Which of the following statements is NOT true to reduce the receiver noise (code) : reduce the loop bandwidth
b.
decrease the predetection integration time
c.
space the early-late correlators closer
d.
increase the signal strength
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a.
Answers : 1. (c) 2. (d) 3. (b) 4. (a) 5. (c) 6. (a) 7. (d) 8. (c) 9. (a) 10. (b) 11. (a) 12. (a) 13. (b) 14. (a) 15. (b) Grade your performance : Excellent (13-15), Very good (11-12), Good (8-10)
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GPS Glossary Glossary of terms : Accuracy : The degree of conformance between the estimated or measured position, time, and/or velocity of a GPS receiver and its true time, position, and/or velocity as compared with a constant standard. Radio navigation system accuracy is usually presented as a statistical measure of system error and is characterized as follows: 1.
Predictable : The accuracy of a radio navigation system’s position solution with respect to the charted solution. Both the position solution and the chart must be based upon the same geodetic datum.
2.
Repeatable : The accuracy with which a user can return to a position whose coordinates have been measured at a previous time with the same navigation system.
3.
Relative : The accuracy with which a user can measure position relative to that of another user of the same navigation system at the same time.
Hi
Analog :
Application software :
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ult
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A type of transmission characterized by variable waveforms representing information, contrasted with digital. A standard clock with moving hands is an analog device, whereas a clock with displayed and changing numbers is a digital device. The human voice and audible sounds are analog. Modem computers are invariably digital, but when they communicate over telephone lines, their signals must be converted to analog using a modem (a modulator/demodulator). The analog signal is converted back into a digital form before delivering it to a destination computer. These programs accomplish the specialized tasks of the user, while operating system software allows the computer to work. A computer-aided dispatch system is application software, as is each word processing program. Automatic Vehicle Location – AVL : A type of system using any sort of technology to track or locate a vehicle. Availability : The percentage of time that the services of a navigation system can be used within a particular coverage area. Signal availability is the percentage of time that navigational signals transmitted from external sources are available for use. Availability is a function of both the physical characteristics of the operational environment and the technical capabilities of the transmitter facilities. Bandwidth : The range of frequencies in a signal.
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Block I, II, IIR, IIF satellites : The various generations of GPS satellites: Block I were prototype satellites that began being launched in 1978; 24 Block II satellites made up the fully operational GPS constellation declared in 1995; Block IIR are replenishment satellites; and Block IIF refers to the follow-on generation. C/A code : The coarse/acquisition or clear/acquisition code modulated onto the GPS L1 signal. This code is a sequence of 1023 pseudorandom binary biphase modulations on the GPS carrier at a chipping rate of 1.023 MHz, thus having a code repetition period of 1 millisecond. The code was selected to provide good acquisition properties. Also known as the "civilian code." Carrier : A radio wave having at least one characteristic, such as frequency, amplitude or phase, that may be varied from a known reference value by modulation. Carrier-aided tracking :
K-
Carrier frequency :
Hi
A signal processing strategy that uses the GPS carrier signal to achieve an exact lock on the pseudorandom code.
Carrier phase :
ns
Co
The frequency of the unmodulated fundamental output of a radio transmitter. The GPS L1 carrier frequency is 1575.42 MHz.
see code division multiple access
ing
CDMA :
ult
GPS measurements based on the L1 or L2 carrier signal.
Channel : A channel of a GPS receiver consists of the circuitry necessary to receive the signal from a single GPS satellite. Chip : The length of time to transmit either a "0" or a "1" in a binary pulse code. Also, an integrated circuit. Chip rate : Number of chips per second. For example, C/A code = 1.023 MHz. Circular error probable (CEP) : In a circular normal distribution, the radius of the circle containing 50 percent of the individual measurements being made, or the radius of the circle within which there is a 50 percent probability of being located.
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Civilian code : See C/ A code. Clock bias : The difference between the clock’s indicated time and true universal time. Clock offset: Constant difference in the time reading between two clocks. Code division multiple access (CDMA) : A method of frequency reuse whereby many radios use the same frequency but each one has a unique code. GPS uses CDMA techniques with Gold's codes for their unique cross-correlation properties. Code phase GPS : GPS measurements based on the C/A code. Computer-aided dispatch :
Control segment :
ns
Co
K-
Hi
An automated system for processing dispatch business and automating many of the tasks typically performed by a dispatcher. Abbreviated CAD (not to be confused with computer-aided design which is also known as CAD) is application software with numerous features and functions. A basic CAD system provides the integrated capability to process calls for service, fleet management and geographical referencing.
ing
Cycle slip :
ult
A world-wide network of GPS monitor and control stations that ensure the accuracy of satellite positions and their clocks. A discontinuity in the measured carrier beat phase resulting from a temporary loss-of lock in the carrier tracking loop of a GPS receiver Data message : A message included in the GPS signal which reports the satellite's location, lock corrections and health. Included is rough information about the other satellites in the constellation. DGPS - see differential positioning? Differential positioning - DGPSA technique used to improve positioning or navigation accuracy by determining the positioning error at a known location and subsequently incorporating a corrective factor (by real-time transmission of corrections or by post processing) into the position calculations of another receiver operating in the same area and simultaneously tracking the same satellites.
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Digital : Generally, information is expressed, stored and transmitted by either analog or digital means. In a digital form, this information is seen in a binary state as a one or a zero, a plus or a minus. The computer uses digital technology for most actions. Dilution of Precision – DOP : A description of the purely geometrical contribution to the uncertainty in a position fix. Standard terms for the GPS application are : GDOP : Geometric (3 position coordinates plus clock offset in the solution) PDOP: Position (3 coordinates) HDOP : Horizontal (2 horizontal coordinates) VDOP: Vertical (height only) TDOP : Time (clock offset only) RDOR Relative (normalized to 60 seconds) Distance root mean square (drms) : The root-mean-square value of the distances from the true location point of the position fixes in a collection of measurements. As typically used in GPS positioning, 2 drms is the radius of a circle that contains at least 95 percent of all possible fixes that can be obtained with a system at any one place. Dithering :
Hi
See dilution of precision Doppler-aiding :
ns
Co
DOP :
K-
The introduction of digital noise. This is the process the DoD used to add inaccuracy to GPS signals to induce Selective Availability.
Doppler shift :
ing
ult
A signal processing strategy that uses a measured doppler shift to help the receiver smoothly track the GPS signal. Allows more precise velocity and position measurement. The apparent change in the frequency of a signal caused by the relative motion of the transmitter and receiver. Earth-centered earth-fixed – ECEF : Cartesian coordinate system where the X direction is the intersection of the prime meridian (Greenwich) with the equator. The vectors rotate with the earth. Z is the direction of the spin axis. ECEF : see earth-centered earth-fixed Elevation : Height above mean sea level. Vertical distance above the geoid.
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Elevation mask angle : That angle below satellites should not be tracked. Normally set to 15 degrees to avoid interference problems caused by buildings and trees and multipath errors. Ellipsoid : In geodesy, a mathematical figure formed by revolving an ellipse about its minor axis. It is often used interchangeably with spheroid. Two quantities define an ellipsoid, the length of the semimajor axis, a, and the flattening, f = (a - b)/a, where b is the length of the semiminor axis. Prolate and triaxial ellipsoids are always described as such. Ellipsoid height : The measure of vertical distance above the ellipsoid. Not the same as elevation above sea level. GPS receivers output position fix height in the WGS-84 datum. Ephemeris : A list of accurate positions or locations of a celestial Object as a function of time. Available as "broadcast ephemeris" or as postprocessed "precise ephemeris." Epoch :
Fast-multiplexing channel : See Fast-switching channel
ns
Fast-switching channel :
Co
K-
Hi
Measurement interval or data frequency, as in making observation every 15 seconds. “Loading data using 30-second epochs” means loading every other measurement.
Frequency band :
ing
ult
A single channel which rapidly samples a number of satellite ranges. "Fast" means that the switching time is sufficiently fast (2 to 5 milliseconds) to recover the data message. A particular range of frequencies. Frequency spectrum : The distribution of signal amplitudes as a function of frequency. Geodesy : The science related to the determination of the size and shape of the Earth (geoid) by direct measurements. Geodetic datum : A mathematical model designed to best fit part or all of the geoid. It is defined by an ellipsoid and the relationship between the ellipsoid and a point on the topographic surface established as the origin of datum.
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Geoid : The particular equipotential surface that coincides with mean sea level and that may be imagined to extend through the continents. This surface is everywhere perpendicular to the force of gravity. Geoid height : The height above the geoid is often called elevation above mean sea level. Geometric Dilution of Precision (GDOP) : See Dilution of Precision GNSS – Global Navigation Satellite System : Organizing concept of a European system that would incorporate GPS, GLONASS, and other space-based and ground-based segments to support all forms of navigation. GPS :
GPS ICD-200 :
Co
K-
Hi
The U.S. Department of Defense Global Positioning System: A constellation of 24 satellites orbiting the earth at a very high altitude. GPS satellites transmit signals that allow one to determine, with great accuracy, the locations of GPS receivers. The receivers can be fixed on the Earth, in moving vehicles, aircraft, or in low-Earth orbiting satellites. GPS is used in air, land and sea navigation, mapping, surveying and other applications where precise positioning is necessary.
Handover word :
ing
ult
ns
The GPS Interface Control Document is a government document that contains the full technical description of the interface between the satellites and the user. The word in the GPS message that contains synchronization information for the transfer of tracking from the C/A to the P-code. Hardware : The physical components of a computer system. Reference is often made to “hardware” and “software”; in that context, “hardware” consists of the computer, input and output devices and other peripheral equipment. Integrity : The ability of a system to provide timely warnings to users when the system should not be used for navigation as a result of errors or failures in the system. Interface : A shared boundary between various systems or programs. An interface is also the equipment or device that makes it possible to interoperate two systems. For example, it is common to interface the 911 telephone system with a computer-aided dispatch (CAD) system. Both hardware and software are needed to provide that interface.
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Ionosphere : The band of charged particles 80 to 120 miles above the earth's surface, which represent a nonhomogeneous and dispersive medium for radio signals. Ionospheric delay : A wave propagating through the ionosphere experiences delay. Phase delay depends on electron content and affects carrier signals. Group delay depends on dispersion in the ionosphere as well and affects signal modulation (codes). The phase and group delay are of the magnitude but opposite sign. Ionospheric refraction : The change in the propagation speed of a signal as it passes through the ionosphere. Kalman filter : A numerical method used to track a time-varying signal in the presence of noise. L-band : The group of radio frequencies extending from 390 MHz to 1550 MHz. The GPS carrier frequencies (1227.6 MHz and 1575.42 MHz) are in the L-band.
K-
Hi
L1 signal :
L2 signal :
ns
Co
The primary L-band signal transmitted by each GPS satellite at 1572.42 MHz. The L1 broadcast is modulated with the C/A and P-codes and with the navigation message.
ing
MDT - Mobile Data Terminal :
ult
The second L-band signal is centered at 1227.60 MHz and carries the P-code and navigation message. A device, typically installed in a vehicle, that consists of a small screen, a keyboard or other operator interface, and various amounts of memory and processing capabilities. Monitor stations : One of the worldwide group of stations used in the GPS control segment to track satellite clock and orbital parameters. Data collected at monitor stations are linked to a master control station at which corrections are calculated and from which correction data is uploaded to the satellites as needed. Multichannel receiver : A receiver containing multiple independent channels, each of which tracks one satellite continuously, so that position solutions are derived from simultaneous calculations of pseudoranges. Multipath : Interference caused by reflected GPS signals arriving at the receiver, typically as a result of nearby structures or other reflective surfaces. Signals traveling longer paths produce higher (erroneous) pseudorange estimates and, consequently, positioning errors.
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Multiplexing channel : A receiver channel through which a series of signals from different satellites can be sequenced. Modem : A modulator/demodulator. When two computers communicate over telephone lines and similar media, digital signals must be converted to analog during transmission, then back again to digital at the destination. Modems are always used in pairs, one at each end. They are rated according to the speed, typically in "bits per second," at which the information can pass through the transmission medium. NAD-83 : North American Datum, 1983 Nanosecond : One billionth of a second. Nav message :
Observation :
Co
K-
Hi
The 1500-bit navigation message broadcast by each GPS satellite at 50 bps on the L1 and/or L2 signals. This message contains system time, clock correction parameters, ionospheric delay model parameters, and the vehicle's ephemeris and health. The information is used to process GPS signals to give user time, position, and velocity.
P-code :
ing
ult
ns
The period of time over which GPS data is collected simultaneously by two or more receivers. The precise or precision code of the GPS signal, typically used alone by U.S. and allied military receivers. A very long sequence of pseudo-random binary biphase modulations on the GPS carrier at a chip rate of 10.23 MHz which repeats about every 267 days. Each one-week segment of this code is unique to one GPS satellite and is reset each week. PDOP - Position dilution of precision : A unitless figure of the merit expressing the relationship between the error in user position and the error in satellite position, which is a function of the configuration of satellites from which signals are derived in positioning (see DOP). Geometrically, PDOP is proportional to 1 divided by the volume of the pyramid formed by lines running from the receiver to four observed satellites. Small PDOP is associated with widely separated satellites. Phase lock : The technique whereby the phase of an oscillator signal is made to follow exactly the phase of a reference signal. The receiver first compares the phase of the two signals, then uses the resulting phase difference signal to adjust the reference oscillator frequency. This eliminates phase difference when the two signals are next compared.
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Point Positioning : A geographic position produced from one receiver in a standalone mode. Precise Positioning Service (PPS) : The highest level of military dynamic positioning accuracy provided by GPS, using the dual-frequency P-code. Pseudolite (shortened form of pseudo-satellite) : A ground-based differential GPS receiver that simulates the signal of a GPS satellite and can be used for ranging. The data portion of the signal may also contain differential corrections that can be used by receivers to correct for GPS errors. PRN - Pseudorandom noise : A sequence of digital 1’s and 0’s that appear to be randomly distributed like noise but that can be reproduced exactly. Their most important property is a low autocorrelation value for all delays or lags except when they coincide exactly. Each GPS satellite has unique C/A and P pseudorandom-noise codes. Pseudorange :
Radionavigation :
Co
K-
Hi
A distance measurement; based on the correlation of a satellite-transmitted code and the local receiver's reference code, that has not been corrected for errors in synchronization between the transmitter's clock and the receiver's clock.
ing
Range rate :
ult
ns
The determination of position, or the obtaining of information relative to position, for the purpose of navigation by means of the propagation properties of radio waves. GPS is a method of radionavigation. The rate of change between the satellite and receiver. The range to a satellite changes due to satellite and observer motions. Range rate is determined by measuring the Doppler shift of the satellite beacon carrier. Relative navigation : A technique similar to relative positioning, except that one or both of the points may be moving. A data link is used to relay error terms to the moving vessel or aircraft to improve real-time navigation. Relative positioning : The process of determining the relative difference in position between two locations, in the case of GPS, by placing a receiver over each site and making simultaneous measurements observing the same set of satellites at the same time. This technique allows the receiver to cancel errors that are common to both receivers, such as satellite clock and ephemeris errors, propagation delays, and so forth. Reliability : The probability of performing a specified function without failure under given conditions for a specified period of time. Scientech Technologies Pvt. Ltd.
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RINEX : Receiver Independent Exchange format A set of standard definitions and formats that permits interchangeable use of GPS data from dissimilar GPS receiver models or postprocessing software. The format includes definitions for time, phase, and range. SA : See selective availability Satellite constellation : The arrangement in space of a set of satellites. In the case of GPS, the fully operational constellation is composed of six orbital planes, each containing four satellites. GLONASS has three orbital planes containing eight satellites each. Selective availability – SA : A DoD program that controls the accuracy of pseudorange measurements, degrading the signal available to nonqualified receivers by dithering the time and phemeredes data provided in the navigation message. Space segment :
Spread spectrum :
Co
K-
Hi
The portion of the GPS system that is located in space, that is, the GPS satellites and any ancillary spacecraft that provide GPS augmentation information (i.e. differential corrections, integrity messages, etc.)
Spherical Error Probable (SEP) :
ing
ult
ns
The received GPS signal is wide-bandwidth and low-power (-160 dBW). The L-band signal is modulated with a PRN code to spread the signal energy over a much wider bandwidth than the signal information bandwidth. This provides the ability to receive all satellites unambiguously and to give some resistance to noise and multipath. The radius of a sphere within which there is a 50 percent probability of locating a point or being located. SEP is the three-dimensional analogue of CEP. SPS : See standard positioning service Squaring-type channel : A GPS receiver channel that multiplies the received signal by itself to obtain a second harmonic of the carriers that does not contain the code modulation. Used in “Codeless” receiver channels. Standard deviation (Sigma) : A measure of the dispersion of random errors about the mean value. If a large number of measurements or observations of the same quantity are made, the standard deviation is the square root of the sum of the squares of deviations from the mean value divided by the number of observations less one.
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Standard Positioning Service (SPS) : The normal civilian positioning accuracy obtained by using the single frequency C/A code. Under selective availability conditions, guaranteed to be no worse than 100 meters 95 percent of the time (2 drms). Static positioning : Location determination accomplished with a stationery receiver. This allows the use of various averaging or differential techniques. SV : Satellite vehicle or space vehicle Universal time coordinated (UTC) : An international, highly accurate and stable uniform atomic time system kept very close, by offsets, to the universal time corrected for seasonal variations in the earth's rotation rate. Maintained by the U.S. Naval Observatory. GPS time is directly relatable to UTC: UTC-GPS = seconds. (The changing constant = 5 seconds in 1988.) URA :
K-
User Interface :
Hi
See user range accuracy
ult
User Range Accuracy-URA :
ns
Co
The hardware and operating software by which a receiver operator executes procedures on equipment (such as a GPS receiver) and the means by which the equipment conveys information to the person using it: the controls and displays.
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The contribution to the range-measurement error from an individual error source (apparent clock and ephemeris prediction accuracies). This is converted into range units, assuming that the error source is uncorrelated with all other error sources. Values < 10 are preferred. User segment : The part of the whole GPS system that includes the receivers of GPS signals. UTC : See universal time coordinated World geodetic system : A consistent set of parameters describing the size and shape of the earth, the positions of a network of points with respect to the center of mass of the Earth, transformations from major geodetic datums, and the potential of the Earth (usually in terms of harmonic coefficients). WGS-84 (World Geodetic System 1984) : The mathematical ellipsoid used by GPS since January, 1987. Y code : The encrypted version of the P-code. Scientech Technologies Pvt. Ltd.
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GPS Acronyms : Bureau des Poids et Measures
C/A
: Code Coarse Acquisition Code
CC
: Composite Clock
CDMA
: Code Division Multiple Access
DGPS
: Differential GPS
DoD
: Department of Defense
DOP
: Dilution of Precision
DoT
: Department of Transportation
FRP
: Federal Radionavigation Plan
GDOP
: Geometric Dilution of Precision
GPS
: Global Positioning System
HDOP
: Horizontal DOP
ICD
: Interface Control Document
IRIG
: Inter-Range Instrumentation Group
L1
: 1575.42 MHz GPS signal
L2
: 1227.6 MHz GPS signal
MC
: Master Control
NAD-27
: North American Datum 1927
NANU
: Notice Advisory to NAVSTAR Users
NTP
: Network Time Protocol
P-code
: Precise-code
PDOP
: Position DOP
PPS
: Precise Positioning Service
PRC
: Primary Reference Clock
PRN
: Pseudo Random Noise
SDOP
: Spherical DOP
SPS
: Standard Positioning Service
SV
: Space Vehicle
TDOP
: Time DOP
USNO
: U.S. Naval Observatory
UTC
: Universal Time Coordinated
VDOP
: Vertical DOP
WGS-84
: World Geodetic System 1984
Y-code
: Encrypted P-code
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Scientech Technologies Pvt. Ltd.
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ST2276
1.
Warranty We guarantee the product against all manufacturing defects for 24 months from the date of sale by us or through our dealers. Consumables like dry cell etc. are not covered under warranty.
2.
The guarantee will become void, if a)
The product is not operated as per the instruction given in the operating manual.
b)
The agreed payment terms and other conditions of sale are not followed.
c)
The customer resells the instrument to another party.
d)
Any attempt is made to service and modify the instrument.
3.
The non-working of the product is to be communicated to us immediately giving full details of the complaints and defects noticed specifically mentioning the type, serial number of the product and date of purchase etc.
4.
The repair work will be carried out, provided the product is dispatched securely packed and insured. The transportation charges shall be borne by the customer.
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Mains Cord .............................................................................................1 No.
2.
RS 232 Cable..........................................................................................1 No.
3.
GPS Antenna .........................................................................................1 No.
4.
e-Manual (Software inclusive) ................................................................1 No.
Scientech Technologies Pvt. Ltd.
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