chapter4 gps

7/28/2019 Chapter4 GPS

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GPS

Vehicle Tracking System

GLOBAL POSITION SYSTEM

4.1 Introduction

The Global Positioning System (GPS ) is a space-based satellite navigation systemthat provides location and time information in all weather conditions, anywhere on or near the Earth where there is an unobstructed line of sight to four or more GPSsatellites.

Each GPS satellite transmits radio signals that enable the GPS receivers to calculatewhere its (or your vehicles) location on the Earth and convert the calculations intogeodetic latitude, longitude and velocity. A receiver needs signals from at least threeGPS satellites to pinpoint your vehicle’s position.

GPS Receivers commonly used in most Vehicle tracking systems can only receive data

from GPS Satellites. They cannot communicate back with GPS or any other satellite.

A system based on GPS can only calculate its location but cannot send it to centralcontrol room. In order to do this they normally use GSM-GPRS Cellular networksconnectivity using additional GSM modem/module.

In this project we use GPS -634R” is a highly integrated smart GPS module witha ceramic GPS patch antenna. The antenna is connected to the module via anLNA. The module is with 51 channel acquisition engine and 14 channel trackengine, which be capable of receiving signals from up to 65 GPS satellites andtransferring them into the precise position and timing information that can beread over either UART port or RS232 serial port. Small size and high-end GPSfunctionality are at low power consumption, Both of the LVTTL level and RS232signal interface are provided on the interface connector, supply voltage of 3.6V~6.0V is supported.

The smart GPS antenna module is available as an off-the-shelf component, 100%tested. The smart GPS antenna module can be offered for OEM applications withthe versatile adaptation in form and connection. Additionally, the antenna can betuned to the final systems’ circumstances.

There are three types GPS of start - hot, warm and cold.

The hot start is when the GPS device remembers its last calculated position and thesatellites in view, the almanac used (information about all the satellites in theconstellation), the UTC Time and makes an attempt to lock onto the same satellites andcalculate a new position based upon the previous information. This is the quickest GPSlock but it only works if you are generally in the same location as you were when theGPS was last turned off.



GPS


The warm start is when the GPS device remembers its last calculated position,almanac used, and UTC Time, but not which satellites were in view. It then performs areset and attempts to obtain the satellite signals and calculates a new position.The receiver has a general idea of which satellites to look for because it knows its lastposition and the almanac data helps identify which satellites are visible in the sky. This

takes longer than a hot start but not as long as a cold start. And finally – the cold start is when the GPS device dumps all the information, attemptsto locate satellites and then calculates a GPS lock. This takes the longest becausethere is no known information.The GPS receiver has to attempt to lock onto a satellite signal from any availablesatellites, basically like polling, which takes a lot longer than knowing which satellites tolook for. This GPS lock takes the longest.



GPS


4.2 FEATURES

• 65 channels to acquire and track satellites simultaneously• Tracking sensitivity reaches -161 dBm• 0.5 PPM TCXO for quick cold start• Integral LNA with low power control • Cold start _ 29 sec under clear Sky• Hot start _ 1 sec under clear Sky• Accuracy 5m CEP • Operable at 3.6V -6V• Both of RS232 and UART interface at CMOS level • Small form factor of 32 mm W x 32 mm Lx 8 mm H• Mountable without solder process • 6 pins wafer connector

4.3 PIN CONFIGURATION



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4.4 General specifications



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4.5 Communication Specification



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4.6 NMEA Protocol

The serial interface protocol is based on the National Marine Electronics Association’s

NMEA 0183 ASCII interface specification. The NMEA 0183 standard uses a simple ASCII, serial communication protocol that defines how data are transmitted in a"sentence" from one "talker" to multiple "listeners" at a time.

Application Protocol Layer rules:

Each message's starting character is a dollar sign. The next five characters identify the talker (two characters) and the type of message

(three characters). All data fields that follow are comma-delimited. Where data is unavailable, the corresponding field remains blank The first character that immediately follows the last data field character is an

asterisk, but it is only included if a checksum is supplied. The asterisk is immediately followed by a checksum represented as a two-

digit hexadecimal number. The checksum is the bitwise exclusiveOR of ASCII codes of all characters between the $ and * . According to the officialspecification, the checksum is optional for most data sentences, but is compulsoryfor RMA, RMB, and RMC (among others).

<CR><LF> ends the message.



GPS


4.6.1 GGA-GLOBAL POSITIONING SYSTEM FIX DATATime, position and fix related data for a GPS receiver.Structure:$GPGGA,hhmmss.sss,ddmm.mmmm,a,dddmm.mmmm,a,x,xx,x.x,x.x,M,x.x,M,x.x,xxxx*hh<CR><LF>

1 2 3 4 5 6 7 8 9 10 11 12 13



GPS


4.6.2 GLL - LATITUDE AND LONGITUDE, WITH TIME OF POSITION FIX ANDSTATUSLatitude and longitude of current position, time, and status.Structure:$GPGLL,ddmm.mmmm,a,dddmm.mmmm,a,hhmmss.sss,A,a*hh<CR><LF>

1 2 3 4 5 6 7 8Example:$GPGLL,4250.5589,S,14718.5084,E,092204.999,A,A*2D<CR><LF>



GPS


4.6.3 GSA - GPS DOP AND ACTIVE SATELLITESGPS receiver operating mode, satellites used in the navigation solution reported by theGGA or GNS sentenceand DOP values.

Structure:$GPGSA,A,x,xx,xx,xx,xx,xx,xx,xx,xx,xx,xx,xx,xx,x.x,x.x,x.x*hh<CR><LF>1 2 3 3 3 3 3 3 3 3 3 3 3 3 4 5 6 7Example:$GPGSA,A,3,01,20,19,13,,,,,,,,,40.4,24.4,32.2*0A<CR><LF>

chapter4 gps

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