GLOBAL POSITIONING SYSTEMPresented by K.MANOJ KUMAR

P.SINDHUSHA

PROBLEMThroughout time people have developed a variety of

ways to figure out their position on earth and to navigate from one place to another.

Later development of artificial satellites made possible Satellites are first used in position finding in a simple

but reliable 2D Navy system called Transit

SOLUTIONIntroducing G.P.SThe Global Positioning System (GPS) is a satellite

based navigation system.The GPS is developed to provide continuous, highly

precise positions, velocity and time information to the land, sea, air and space based users

combination of ground stations, orbiting satellites and special receivers to provide navigation capabilities to virtually everyone, at anytime, anywhere in the world, regardless of weather conditions.

 

ABSTRACT The search for a better and an accurate option resulted in the GLOBAL

POSITIONING SYSTEM (GPS), a system that’s changed navigation forever.

The GPS is a worldwide radio-navigation system formed from a constellation of 24 satellites and their ground stations. The GPS is a worldwide radio-navigation system formed from a constellation of 24 satellites and their ground stations.

The three segments are User segment, Space Segment and Control Segment.

INTRODUCTION GPS is comprised of three segments: satellite

constellation, ground-control/monitoring network, and user receiving equipment

The satellite constellation is the set of satellites in orbit that provide the ranging signals and data messages to the user equipment

The control segment (CS) tracks and maintains the satellites in space.

Furthermore, the CS updates the satellite clock corrections and ephemerides as well as numerous other parameters essential to determining user PVT

SEGMENTS OF G.P.SSpace Segment OverviewUser Segment OverviewControl Segment (CS) Overview

SPACE SEGMENT OVERVIEW

This concept makes GPS a passive system for the user with signals only being transmitted and the user passively receiving the signals.

An SV includes payloads and vehicle control subsystems. The primary payload is the navigation payload used to support the GPS PVT mission

The vehicle control subsystems perform such functions as maintaining the satellite pointing to Earth and the solar panels pointing to the Sun.

CONTROL SEGMENT(CS)OVERVIEW The CS is responsible for maintaining the satellites and their proper

functioning. This includes maintaining the satellites in their proper orbital positions (called station keeping)

The CS updates each satellite’s clock, ephemeris, and almanac and other indicators in the navigation message at least once per day.

The ephemeris parameters are a precise fit to the GPS satellite orbits and are valid only for a time interval of 4 hours with the once-per day normal upload schedule

The almanac consists of 7 of the 15 ephemeris orbital parameters.

Furthermore, the CS resolves satellite anomalies, controls SA and AS, and collects pseudo range and carrier phase measurements at the remote monitor stations to determine satellite clock corrections, almanac, and ephemeris.

USER SEGMENT OVERVIEW The user receiving equipment comprises the

user segment. Each set of equipment is typically referred to as a GPS receiver, which processes the L-band signals transmitted from the satellites to determine user PVT.

WORKING Most modern GPS receiver designs are digital receivers. These receiver

designs have evolved rapidly toward higher and higher levels of digital component integration, and this trend is expected to continue

. For this reason, a high-level block diagram of a modern generic digital

GPS receiver will be used to represent a generic GPS receiver architecture

These RF signals are amplified by a low noise preamplifier (preamp), which effectively sets the noise figure of the receiver.

These amplified and signal conditioned RF signals are then down-converted to an IF using signal mixing frequencies from local oscillators (LOs).

Two-stage down-conversion to IF is typical, but one-stage down-conversion and even direct Land digital sampling have also been used

The A/D conversion process and automatic gain control (AGC) functions take place at IF.

The IF must be high enough to provide a single-sided bandwidth that will support the PRN code chipping frequency.

The signals from all GPS satellites in view are buried in thermal noise at IF No demodulation has taken place, only signal gain and conditioning plus

A/D conversion into the digital IF

HOW DO SATELLITE DETECT THE OBJECT The name digital receiver channel is somewhat misleading since it is

neither the ASIC nor FPGA but the receiver processing function that usually implements numerous essential but complex (and fortunately less throughput-demanding) baseband functions, such as the loop discriminators and filters, data demodulation, SNR meters, and phase lock indicators.

The whole idea behind GPS is to use 24 satellites in space as reference points for locations here on earth.

Knowing that we're 11,000 miles from a particular satellite narrows down all the possible locations we could be in the isle is aliased into the GPS signal pass band by the A/D conversion process whole universe to the surface of a sphere that is centered on this satellite and has a radius of 11,000 miles as shown in the following Fig.

•Let the distance from second satellite is 12,000 miles, then we're somewhere on the circle where these two spheres intersect as shown in the following Fig.  Even though there are two possible positions, they differ greatly in longitude/latitude position and altitude. To determine which of the two common points our actual position is, we’ll need to enter our The Pseudo Random Code (PRC)

•It is a fundamental part of GPS. The signal is so complicated that it almost looks like random Electrical noise. Hence the name "Pseudo-Random”. Physically it's just a very complicated digital code. It’s just a complicated sequence of "on" and "off" pulses as shown here. Approximate altitude into the GPS receiver. This will allow the receiver to calculate a two dimensional position (latitude, longitude). However, by adding a fourth satellite, the receiver can determine our three dimensional position (latitude, longitude, altitude)

Even though there are two possible positions, they differ greatly in longitude/latitude position and altitude. To determine which of the two common points our actual position is, we’ll need to enter

     The Pseudo Random Code (PRC)

It is a fundamental part of GPS. The signal is so complicated that it almost looks like random Electrical noise. Hence the name "Pseudo-Random”. Physically it's just a very complicated digital code. It’s just a complicated sequence of "on" and "off" pulses as shown here. Approximate altitude into the GPS receiver. This will allow the receiver to calculate a two dimensional position (latitude, longitude).

RANGING CALCULATIONS

Pseudo-Random Code also guarantees that the receiver won't accidentally pick up another satellite's signal

All the satellites can use the same frequency without jamming each other.

The complexity of the Pseudo Random Code makes GPS economical. The codes make it possible to use "information theory" to "amplify" the GPS signal.

TRACKINGThese are some of the more advanced tools

available in GPS Utility.

Generate search patterns, e.g. rectangular, zigzag, square, area search. and so on – such patterns can then be loaded directly into your GPS.

CONCLUSIONThough originally designed to help US Forces

around the world to locate targets and move quickly, it is now being used across the world, from mountaineers climbing up Mount Everest to sail boats journeying in to oceans. Its functions have been extended to over positioning, tracking, mapping etc. GPS’s future seems secure. Its biggest push now is the Federal Communications Commission (FCC) enhanced 911 mandates.

The GPS satellites, like handmade stars in the sky, will be guiding us well into the 21st century.

THANK

U