GLOBAL POSITIONING SYSTEM (GPS)

A Survey Submitted for the requirement of knowledge & practice in report-making in

(ELECTRONICS AND COMMUNICATION ENGINEERING)

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Submitted ToMr.Sumit DhandaLecturer,Department of Electronics & Communications Engineering

Submitted ByAman GoelAUR1062002

CERTIFICATEIt is certified that the survey entitled “GLOBAL POSITIONING SYSTEM (GPS)” submitted by

Aman Goel with Enrolment No. (A20422210010) on (October 2014) in Electronics and

Communication Engineering of Amity University Rajasthan, Jaipur during the academic year

2014-2015, is his own work and has been carried out under my supervision. The results

embodied in this report have not been submitted to any other University or Institution.

Mr. SUMIT DHANDA AMAN GOEL

Signature: Signature:

DATE:

DESIGNATION: Lecturer, E.C.E Dept.

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ACKNOWLEDGEMENT

It is a pleasure to thank the following whose words were a great encouragement to me in the

preparation on this survey: Mr. Sanyog Rawat, HOD (E&C), Amity University Rajasthan; and

my faculty guide, Mr. Sumit Dhanda, Amity University Rajasthan.

Finally, I want to thank my family and friends for constant encouragement and support.

AMAN GOEL

B.Tech + M.Tech (E.C.E) – VIIIth SEM

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ABSTRACT

Global Positioning System (GPS) has been a very useful tool for the last two

decades in the area of geodynamics. The modest budget requirement and the

high accuracy relative positioning availability of OPS increased the use of it in

determination of crustal and/or regional deformations. Since the civilian use to

the GPS beggar: in 1980. The development on the receiver and antenna

technology with the ease of use software packages reached to a well-known

state, which may be named us a revolution in the Earth Sciences. ’The process of

GPS measurements has mostly studied subject since GPS was started to use by

civilian users. In this respect, scientific software has heer: developing such as

GAMIT! GLOBK well-known all around the world. GPS measurements are used to

obtain the information of the strain accumulation along fault lines. In addition,

GPS measurements offer a magnificent tool for measuring tectonic strain rates,

which are assumed to be indicative of earthquake potential. Generally in

geodynamic, GPS measurements can be examined in two main branches as

continuous and campaign measurements. Firstly, there are great deals of

networks observed data continuously all over the world.

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TABLE OF CONTENT_ PAGE NO.CERTIFICATE 2

ACKNOWLEDGEMENT 3

ABSTRACT 4

TABLE OF FIGURE 6

1. INTRODUCTION 7

2. HISTORY OF GPS 9

3. CURRENT ISSUES 10

3.1. A Vision for GPS 10

3.2. Military Effectiveness Issues 11

3.3. Lack of Balance among the GPS Segments 11

3.4. GPS III Satellite 12

4. SYSTEM ARCHITECTURE 14

5. EFFECTS OF RADIO FREQUENCY INTERFERENCE

ON GPS SIGNALS 17

6. MONITORING NETWORKS 18

6.1. DOD Monitoring Networks 18

6.2. Civil Monitoring Networks 19

7. References 21

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LIST OF FIGURE_ PAGE NO.

Fig 1: GPS operations 8

Fig 2: GPS Instrumented Vehicle System Architecture 15

Fig 3: DOD Monitor Stations 19

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CHAPTER 1 - INTRODUCTION

Many different on-road vehicle systems exist or are being developed to address

individual Department of Transportation applications such as lane-keeping,

lateral collision avoidance, intersection collisions, route planning, traffic

management, collision notification, automated control, etc. Each of these

systems varies in performance and implementation challenges. Both commercial

and government activities continue to address the problem of combining

systems designed for specific applications to provide a low cost, integrated

vehicle system which can significantly increase driver and vehicle safety. GPS has

Significant potential for enabling a variety of transportation user services.

Standard commercial products support civilian Coarse/Acquisition (C/A) code

GPS which provides position accuracy on the order of 30-50 meters Circular

Error Probability (CEP), due primarily to Selective Availability (SA). The

application of Differential GPS (DGPS) using a low cost GPS receiver can result in

position accuracy on the order of 1-5 meters. DGPS involves the broadcasting of

navigation data and measurements or corrections from a surveyed base station.

This approach can mitigate the effect of common error sources.

A wide range of transportation applications can be supported with a single,

configurable, on-board vehicle system. Some of the applications, such as route

planning, collision notification, and traffic management require easily achieved

position accuracies on the order of 10-30 meters; however, applications such as

lane-keeping, collision avoidance, impaired driving detection, and automated

vehicle control require real-time precise positioning and a precision reference

map. For example, the lane-keeping application requires accuracy on the order

of a few centimeters to identify imminent lane departures early enough such 7

that the operator can take preventative measures. If multiple vehicles applied a

precision positioning system with two-way communications, their positions

could be broadcast to other vehicles in the immediate vicinity. These positions

could be tracked by software on-board the vehicles to support warning the

operators of potential collisions. Monitoring accurate vehicle positions over time

and comparing to nominal driver behavior could provide a measure of driver

effectiveness. For real-time vehicle control, the precise position information

could be used with surveyed map data and vehicle control actuators to support

navigation. Even though the same accuracy is not required, the position

information and two-way communications could be used to support route

planning, collision notification and traffic management as well. A properly

designed, in-vehicle, GPS-based system can support all actions at a high level of

accuracy and provide a robust, all weather alternative to other sensor systems

being considered. An integrated GPS system appears to offer the capability to

support positioning requirements of most advanced driver support systems

envisioned for the “intelligent” vehicles of the future, --private automobiles,

commercial and transit vehicles.

Fig 1: GPS operations

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CHAPTER 2- HISTORY OF GPS

Throughout time people have developed a variety of ways to figure out their

position on earth and to navigate from one place to another. Early mariners

relied on angular measurements to celestial bodies like the sun and stars to

calculate their location. The 1920s witnessed the introduction of a more

advanced technique radio navigation—based at first on radios that allowed

navigators to locate the direction of shore-based transmitters when in range.1

Later, the development of artificial satellites made possible the transmission of

more-precise, line-of-sight radio navigation signals and sparked a new era in

navigation technology. Satellites were first used in position finding in a simple

but reliable two-dimensional Navy system called Transit. This laid the

groundwork for a system that would later revolutionize navigation forever—the

Global Positioning System.

The GPS is a space-based positioning, navigation and timing (PNT) system

developed by the DOD and currently managed by the U.S. government through

an interagency process that seeks to fuse civilian and military interests. The U.S.

Air Force finances and operates the system of 24+ GPS satellites (distributed in

six orbital planes) and a control segment with associated ground monitoring

stations located around the world. GPS signals permit simultaneous

determination of both precise three-dimensional position and precise time. GPS

was the first and remains the only global, three-dimensional radio navigation

and timing system providing continuous operational service today.

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CHAPTER 3 – Current Issues

Sustaining GPS Contributions Requires Prompt Leadership Attention -- From all

outward appearances, GPS seems to be a healthy, successful program. At its

current level of performance, GPS is providing, on average, better than 5-meter

horizontal accuracy, better than 10-meter vertical accuracy and absolute time

within 0.1 microsecond of Universal Coordinated Time (UTC). With differential

GPS techniques, local accuracies of 1-meter and better are routine. However,

our investigation into various aspects of GPS operation and management reveals

serious issues that affect its operational viability and require prompt leadership

action to correct. These include issues of military effectiveness, civil

performance and competitiveness, and governance.

3.1 A Vision for GPS

GPS has been implemented and operated to this point without benefit of a

commonly accepted vision of its potential contributions. Even so, it has

produced dramatic improvements both globally and for our nation that

exceeded the expectations of its creators. Those achievements have occurred

largely because of consistent support provided to GPS by the civilian leadership

in the DOD and despite the fact that we may have forgone opportunities for

more rapid improvement. For the future, post-2020, it should be apparent from

our experience thus far that GPS can continue to improve quality of life and

performance to the extent that opportunities for those improvements continue

to be incorporated into its total system design within the global PNT

architecture. GPS initiatives for the future should focus on proactive

improvements to GPS service fidelity and robustness to continue expanding its 10

performance benefits while protecting against possible asymmetric attacks

directed at GPS enhanced infrastructure components.

3.2 Military Effectiveness Issues

Improvements Needed, Implementation Lacking – While GPS has proven itself

technically effective in meeting military mission requirements in general, it is

neither robust enough to overcome credible jamming threats nor are the

military signals available in sufficient quantity to meet warfighter needs under

many likely operational scenarios. Operational control and equipment

acquisition strategies now being executed are insufficient to address these

deficits as rapidly as necessary. The warfighter leadership is becoming more

aware of the extent to which GPS is integral to individual mission concepts of

operation and operational architectures. However, this growing level of

awareness has yet to translate into accelerated implementation, or even plans

for implementation, of the GPS improvements necessary to effectively support

those missions and architectures in the future. The Task Force finds this lack of

improvement to be unsatisfactory, and has included recommendations to

stimulate proactive planning for GPS improvements within the operational

planning process.

3.3 Lack of Balance among the GPS Segments

Balance situation has occurred for a variety of reasons, primarily related to

technical issues and funding. Since the satellites are the critical signal sources

and even new satellites can be operated by the existing control segment to

maintain legacy services, they have taken priority when technical problems arise

that endanger future launch schedules. In some cases, those problems have

required diversion of funding from the other segments, causing delays in their

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improvement and evolution. One operational capability that has been

particularly affected has been anti jamming performance, which requires both

control and user segment improvements to take advantage of new satellite

signals. Additionally, diversion of funding from user equipment development

delays other improvements in signal processing that can provide anti-jam

improvements independent of new satellite signals.

3.4 GPS III Satellite

The GPS III satellite is still undergoing design by two contractor teams (led by

Boeing and Lockheed-Martin/Spectrum Astro). Block III satellites will

incorporate improved electronics, high data rate crosslinks (high

frequency/narrow beam) providing continuous contact among satellites, and a

high power spot beam (“theater” size) for anti-jam improvement. The spot

beam is intended to meet the JROC-endorsed anti-jam requirement for +20 dB

signal strength improvement by providing additional power directly from the

satellites in lieu of making substantial changes to user equipment antennas and

processing technology. First launch for the GPS III satellite was originally planned

for FY09 with fully populated constellation by 2016/17; however, go-ahead

delays and funding shortages elsewhere in the program have delayed the first

launch until at least FY13. The new capabilities, when added to the existing

primary and secondary payloads, represent additional cost and weight for the

GPS III satellites. Original GPS Block II-version satellites cost on the order of $30+

million. With improvements to signal structure and power (taking account of

effects of sole source contracts and low quantities) Block IIR-M and Block IIF

satellites now cost on the order of $60-80 million. Even at those prices, the Air

Force has experienced difficulty in procuring sufficient satellites and medium-lift

boosters to assure the 24-satellite constellation can be sustained at a high level

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of probability into the future. Block III satellites are anticipated to cost on the

order of $100-150 million. Based on these projections, the Task Force considers

it essential that the Air Force investigate alternatives to lower total constellation

on-orbit costs. Such alternatives include deletion of secondary payloads with

significant weight and power needs from some or all GPS satellites and

operating a mix of spot-beam satellites and higher power earth coverage

“utility” satellites with lower relative cost/complexity.

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CHAPTER 4 – System Architecture

Preliminary lane-keeping concepts for position sensor technologies,

infrastructure or implementation issues, and system configurations were

investigated. The architecture developed for this project was based on

convenience and utilization of existing assets vice optimization of the prototype

system. Detailed prototype system issues including the use of multiple base

station data, mobile GPS reference station separations, communications,

antenna selection, wider survey maps, improved navigation system

architectures were outside the scope of this project.

An Integrated system architecture, using DGPS and navigation aids to calculate

real-time vehicle position, is given in Figure 2. A real-time data collection system

was developed on the Instrumented Vehicle to acquire DGPS, odometer,

heading, tilts, inertial navigation measurement, gyroscope, and video camera

data. In this implementation, the system directly applies the position

information as provided by the receiver. GPS position and velocity data, select

navigation aids (odometers, vehicle heading, vehicle tilts) and vertical map

measurements (from the surveyed reference map) were integrated using an

Extended Kalman filter to smooth through GPS signal dropouts. This serves to

enable vehicle navigation during GPS blockage with graceful performance

degradation. Data from the navigation aids were analyzed to determine the

optimal configuration of sensors to smooth through data dropouts. Data was

collected to evaluate several GPS hardware configurations to determine an

initial system approach that would increase the reliability of the position data. A

video camera was used to view the lane markings in order to provide an

independent observation of lane departures and to assist in mapping the road 14

boundaries. An accurate survey and map representation approach was

developed using the same vehicle and roadside instrumentation. In view of the

logistics and costs associated with travel to remote test sites, a local road was

mapped and used as the only test site. A user interface for lane departure and

warning capability was developed. Prototype real-time software was developed

and integrated into an overall system design for the vehicle positioning system.

Near real time post-run analysis capability was used to quickly evaluated system

performance for demonstration purposes. All vehicle and roadside GPS range

and range rate data were recorded from all receivers for post-test evaluation of

data consistency and modeling, and evaluation of the COTS real-time GPS only

performance. Also, other unutilized navigation sensor data (i.e. IMU data) were

recorded to evaluate the improvement in position updates between GPS signal

blockages and to provide a more robust real-time indication of lane departures.

Fig 2: GPS Instrumented Vehicle System Architecture

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The Instrumented Vehicle data acquisition system is built around a Pentium

18OMhz processor running Windows 95 and equipped with several PCI cards

used to acquire serial (RS232) and analog sensor outputs. This system is also

equipped with several PCI cards used to acquire serial and analog sensor

outputs. The data acquisition software was developed using National

Instruments Labview graphical programming language. The data acquisition

software samples and records four channels of serial data and seven channels of

analog data. .The IMU and TCM2 are polled (synchronous) sensors and transmit

their serial data packets at 10Hz. The AUTOGYRO and DGPS (Ashtech 2-12) are

asynchronous. The AUTOGYRO uses an intimal clock to transmit its serial data at

10 Hz and the DGPS receiver transmits a serial data packet at 2Hz, on the even

second and half-second mark. The IMU also provides its output in an analog

format. These six analog outputs are recorded using the National Instruments

PCI-MIO-16XE board at a 10 Hz sampling rate. The wheel turns are recorded

using a timer counter chip on the MI0 board to clock the input pulses and

develop an integer wheel count. The Time code interface is used to provide an

accurate timing environment for the acquisition and file subsystems. The DGPS

supplies an lpps signal used by the time code interface to provide the system

synchronization. The system is operated using a graphical user interface, which

allows the user to control and configure serial analog inputs, digital signal

inputs, the TCP/IP connection to the Kalman Filter Processing computer,

program execution, data recording and real-time data monitoring. The data is

both recorded to hard disk as well as sent via a TCP/IP interface to the Kalman

Filter Processor.

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CHAPTER 5 – Effects of Radio Frequency Interference on GPS Signals

The effect of radio frequency interference (RFI) on the GPS signals could also

degrade accuracy and, in worst case scenarios, cause loss of tracking of GPS

signals. Although there have been a number of studies concerning this topic,

their investigations towards GPS accuracy are somewhat tricky and need

continuous observations. This situation happened due to other error parameters

that existed in tandem with RFI. All of these errors have their own intent; to

corrupt GPS measurements. There are two general types of RFI known as

unintentional and intentional RFI. Usually, unintentional interference is caused

from the natural occurrences of RF transmitting systems (e.g., satellite

communication, television broadcasting, radar application, and ultra wideband

communication) which can interfere with GPS frequency bands. Meanwhile,

intentional jamming is defined as the broadcasting of a strong signal that

overrides or overwhelms the signal being jammed. GPS signals that reach the

Earth are vulnerable to various probable errors, including RFI, due to their weak

power levels, in the range of -160 - -130 db. These low power levels can cause

GPS signals to be swamped by relatively low powered interference signals, even

though they are well below the noise floor. GPS interference signals, which are

in the range or near the GPS frequency bands, can from either intentional or

unintentional sources.

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CHAPTER 6 – Monitoring Networks

6.1 DOD Monitoring Networks

The MCS receives continuous information regarding GPS military signal fidelity

through a global network of six dedicated monitor stations, identified above.

Each monitor station receives the Y-Code signals from whichever satellites are in

view, and most of the constellation is in view of at least one monitor station at

all times. The exception is that satellites whose orbits take them below the

equator in the eastern South Pacific may be out of view by any monitor station

or uplink antenna for 20 minutes or more. An initiative was undertaken in 1995

to mitigate this situation by incorporating data from monitor stations operated

by the National Geospatial-Intelligence Agency (NGA) at locations that would fill

the gap and augment other observations. However, funding for this effort, called

the Accuracy Improvement Initiative (AII), was insufficient to integrate the NGA

data into MCS software until this year when data from an initial six NGA stations

will be incorporated. Data from five more NGS stations is planned to be

incorporated in 2006 (Figure 3).

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Fig 3: DOD Monitor Stations

6.2 Civil Monitoring Networks

In addition to monitor stations operated by the DOD, there are separate

regional and global networks of civil signal (C/A-Code) monitor stations

operated by government and scientific organizations. Global networks include

the Global Differential GPS (GDGPS) System and the International GPS Service

(IGS).

The GDGPS is operated by the Jet Propulsion Laboratory (JPL) with funding from

NASA and others and gathers data from over 60 worldwide monitoring stations

(see Figure 4). Raw data from the GDGPS provide the basis for a value-added

commercial differential GPS service called GreenStar, offered by John Deere and

furnishing high precision GPS augmentation for precision farming. The GDGPS

System is completely independent of the GPS OCS infrastructure, thus increasing

the probability of detecting an anomaly. The system has demonstrated

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extremely high reliability since its inception in early 2000. An integrity

monitoring prototype based on the GDGPS System was developed in

collaboration between JPL and the Aerospace Corporation, and was launched in

May 2003. It provides secure internet access to authorized users, including

2SOPS operators from the MCS floor as well as from their homes. The

developers at NASA/JPL and Aerospace are now in the process of implementing

end-to-end secure data authentication, and automated alarms with 4 second

latency. Feedback from the MCS indicates that the system is a very valuable

tool.

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REFERENCES

1. Applications of Global Positioning System (GPS) in Geodynamics

H.Yavasoglu’, E.Tari’, M. Sahin’, H. Karaman’, T. Erden’, S. Bilgi], S.

Erdogan’ ’ Istanbul Technical University Department of Geodesy and

Photogrammetry. sahin(i?itu.edu. tr, vavasoeluG:itu.edu. ti 34469

MaslaWIstanbul, Turkey ’ Afyon Kocatepe University Department of

Geodesy and Photogrammetry Ahmet Necdet Sezer Campus 03 100,

Afyon, Turkey.

2. Effect of Radio Frequency Interference (RFI) on the Global Positioning System

(GPS) Signals

Ahmad Norhisyam Idris, Azman Mohd Suldi & Juazer Rizal Abdul Hamid

Centre of Studies Surveying Science and Geomatics Faculty of

Architecture, Planning and Surveying, UiTM Shah Alam, Malaysia

syam.uitm@gmail.com,azmansuldi@gmail.com,juazer@salam.uitm.edu

3. Defense science board task force on future of the global positioning system.

4. GPS Roadside Integrated Precision Positioning System

David Hohman, Thomas Murdock, Edwin Westerfield, Thomas Hattox, and

Thomas Kusterer, The Johns Hopkins University, Applied Physics

Laboratory david.hoh”@jhuapl.edu.

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