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GLOBAL POSITIONING SYSTEM (GPS)
A Survey Submitted for the requirement of knowledge & practice in report-making in
(ELECTRONICS AND COMMUNICATION ENGINEERING)
1
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
[email protected],[email protected],[email protected]
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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