International Journal of Technical Research and Applications e-ISSN: 2320-8163,
www.ijtra.com, Special Issue 42 (AMBALIKA) (March 2017), PP. 117-120
FUSION OF GLOBAL POSITIONING SYSTEM
AND INERTIAL NAVIGATION SYSTEM: A
REVIEW
1
1
Vertika Verma, 2 Wg. Cdr. (Retd) Dr. Anil Kumar
Department of Electronics and Communication Engineering Amity University,Lucknow
2
Director,ASET,Amity University, Lucknow
1
[email protected],[email protected]
Abstract— In this paper a study of general concepts of Global
Positioning system fusion with Inertial Navigation has been
carried out. Location and time information is provided by GPS
as long as there is unobstructed line of sight to four or more GPS
satellite.However, when line of sight is not clear the signal may
inaccurate, sometimes completely blocked. In such situation
Inertial Navigation System is appropriate choice for positioning.
The GPS satellite Signals is used in integrated GPS- INS to
correct or calibrate a solution from an inertial navigation system.
There are two methods proposed for GPS/INS integration. One
based on a bank of parallel running Kalam filter and the other
based on an adaptive observer.
Index Terms— fusion of global inertial navigation system.
A satellite based navigation system Global Positioning system
is made of network of 24satellites placed into orbit by U.S
Defence Department. Location and time information is
provided by it in all weather conditions anywhere near or on
earth. It works well were there in no obstruction in line of sight
to four or more satellites. However in case of obstruction eg
forests,indoors,heavily built urban areas etc,it may not work
well and provide inaccurate location information. In this
situation to obtain accurate location one uses other devices or
sensors for example accelerometers, gyroscopes and
magentometers.Those sensors together with algorithm for
object’s positions constitute main part of the Inertial
Navigation System that will used in project.
I. INTRODUCTION
Fusion of INS and GPS has been used in last couple decade to
span different systems. Ship, aircraft and submarine Navigation
systems are just some of the most common applications. Most
of the applications will struggle
for
following
two
characteristics:
1) Continuous and reliable navigation determination.
2) Acceptable accuracy level and possibility to keep accuracy
over time.
II. GLOBAL POSITIONING SYSTEM
Global Positioning System consists of three major segments
known as space segment,the control system and the user
segment which is also known as receiver.
INS provides continuous and reliable navigation determination
but errors in them increases over time due to algorithm they
use. Instead GPS can be used as an aiding system in order to
minimize the errors over time updating the position and
velocity as often as possible.The main reason for integrating
INS and GPS is therefore done in order to get a system that can
achieve both above mentioned characteristics.
Fig 1. Diagram of GPS
The accuracy needed can vary a lot between each application.
Navigation systems for autonomous car and aircraft may
require sub-meter level accuracy while others like car
navigation systems only needs 10-30 meter of accuracy in
order to achieve its goal. Most of the accuracy is determined
by equipment used in INS and
GPS.Especially the performance from different inertial
senors can vary a lot and low cost INS systems may result in
errors upto many thousands of meters in just a few stand alone
mode.
A. Space Segment
Presently GPS Space Segment comprises a constellation of 24
operational Navstar satellelite.These satellites orbit the earth
with a period of one-half a sidereal day, which is 11 hour 58
minutes to be precise, in nearly circular orbit of radius
approximately 26560 km from centre of the earth. This is an
altitude of approximately 20,200Km.There are six orbital
planes with four satellites in each plus four orbital spares. The
full constellation ensures global coverage with 6 to 11
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International Journal of Technical Research and Applications e-ISSN: 2320-8163,
www.ijtra.com, Special Issue 42 (AMBALIKA) (March 2017), PP. 117-120
simultaneously observable satellites to users located anywhere
in the world at any time of day, thus ensuring considerable
satellites considerable satellites continuously transmits coded L
band radio signals that the receiver will decode to determine
important satellite parameters. The receiver tracks RF signals
of selected satellites and calculates three dimensional
navigation data and time.The satellites have various
identification such as (i) Launch sequence number (ii)Assigned
vehicle Pseduo Radom Noise(PRN)code(iii)Orbital position
number(iv)Catalogue number (v)International designation and
so on. Each satellite carries a highly accurate Cesium or a
Rubidium atomic clock to provide timing for satellite signals
.Internal clock correction is provided for each satellite clock.
All components are precisely controlled by the atomic clock.
All signal components are precisely controlled by the atomic
clock. The satellite employs transmitting antenna whose shapebeam gain uniform power to system users.
B. Control Segment
The control comprises a Master Control Station(MCS),an
alternate master control station, six worldwide monitor stations
and four dedicated ground antenna stations. The ground
monitoring stations measure signals from overhead satellites at
fixed interval of time and corrected data is transmitted to
master control station.MCS determines the orbital model ,clock
performance and health of the satellites and these are then
delayed to the uplink ground antennas for transmission to
satellites ,which is further broadcast to the user segment.The
main operations and tasks of MCS can be listed as:
(a) Tracking of satellites
(b) Orbit determination
(c) Prediction,modelling and time synchronisation of satellites
(d) Upload of data for broadcast to the user segment
(e) Monitoring the health status of the satellites
C. User Segment
The user segment, normally called a receiver , consists of an
antenna along with the receiver electronics that receives and
decodes satellite transmissions. The receiver also converts
satellite signals to computed position , velocity and time
(P,V,T) estimates. The receiver performs the following primary
task:
(a)Selection of one or more satellites
(b)To acquire satellite signals, measuring the range to the
satellite and tracking more satellites
(c)Processing of measurements in real time to compute
navigational data in a navigation frame that is needed by the
user application.
The receiver maintains a time reference used to generate a
replica of the code transmitted by the satellite. The amount of
time the receiver must apply to correlate the replica with the
satellite clock referenced code received from the satellite,
provided a measure of the signal propagation time between the
satellite and the receiver. This time when multiplied by the
velocity of light provides the range distance.
III. INERTIAL NAVIGATION SYSTEM
An INS is a navigation system that uses accelerometers and
gyroscopes to calculate(with dead reckoning or integration of
accelerometers) the position, velocity, acceleration and
orientation of an object of interest. Two big advantages of an
INS is that it uses no external measurement (except for (expect
for initializing) for positioning and is it immune to jamming. It
is commonly used in aircraft, missiles and spacecraft. An
drawback of INS is the drift error that will accumulate with
time and thus positioning information will be in accurate. A
sensor that is commonly with INS to solve this problem is
magnetometer The magnetometer provide heading information
and the magnetometers’ heading information can be fused
together with the INS to provide better position estimation. The
INS that has been used in this project is based on a previous
master thesis and a report is recommended for further
information about the INS. This chapter provide some brief
information about the INS used in this project
IV. GPS/INS INTEGRATION
The system is made up of two systems, one called Dead
Reckoning Module (DRM) which is an INS system that uses
accelerometers, gyroscopes
and magnetometers to
provide a position information for a (in our case) pedestrian.
The other system is the GPS. The objective of integrating these
two systems is to provide a better estimation of the position.
INS/GPS integration can provide a better estimation of the
position than each of the systems used. It utilizes the strengths
of the bounded error of the GPS and the short term accuracy
from the INS. A normal basic approach is to let INS provide
the model and trajectory, while the GPS measurements serve as
the update measurement. There are four different ways to
approach INS/GPS integration: uncoupled, loosely coupled,
tightly coupled and ultra tightly coupled.
A. Uncoupled Approach
Uncoupled approach is probably the simplest one to INS/GPS
integration. It uses the position and velocity estimated by the
receiver to, in some intervals of time, update the INS estimated
position. Although this is the simplest method to apply it does
not provides any possibility for either GPS outage detection or
jamming detection. Also, when less than 4 satellites are
available the system performance decreases apace.
Fig-2 Illustration of Uncoupled Approach
B. Loosely Coupled Approach
The loosely coupled approach is using two filters to provide an
estimate of the receivers position. The first filter is operating in
the GPS receiver. It uses raw data from the satellites to
estimate the position and velocity. Parallel is a mechanization
118 | P a g e
International Journal of Technical Research and Applications e-ISSN: 2320-8163,
www.ijtra.com, Special Issue 42 (AMBALIKA) (March 2017), PP. 117-120
process working, estimating the velocity and position of the
INS. A second filter is then applied to fuse the GPS position
and velocity with the INS position and velocity. The
information about the estimated position is then used to update
the INS position. The benefit of using loosely coupled is both
that it is robust since it uses two diff erent systems to
estimate the position, as well as it can be applied to any INS
and GPS receiver. The two system also make the loosely
coupled approach suitable for GPS fault detection Fig3
illustrates the loosely coupled approach.
Fig.3 Loosely Coupled Approach
C. Tightly coupled and ultra tightly coupled approach
The last two approaches are the tightly and ultra tightly
coupled approaches. Those two approaches combine the raw
GPS measurements with the raw sensor measurements from
the INS, in a single filter. Information to update the sensor
values are then transferred back to both the INS and GPS. This
approach provides a better estimation than the loosely coupled
approach, since the signals coming from the GPS part will not
be as correlated as in the loosely coupled approach. This
method may also works with as many as one satellite
V. APPLICATIONS
GPS/INS fusion is mostly used on aircraft for navigation. Use
of GPS/INS allows for smoother position and velocity
estimates that provides sampling rate faster then GPS
receiver.It also allows for accurate estimation of the aircraft
attitude (roll, pitch, and yaw)[citation needed] angles. GPS/INS
sensor fusion is a nonlinear filter problem, which is commonly
approached using the extended Kalman filter (EKF) or the
unscented Kalman filter (UKF). The use of these two filters for
GPS/INS has been compared in various sources, includes
analysis of sensitivity. The analytical linearization approach is
used in EKF using Jacobian matrices to linearize The system,
while the UKF uses a statistical linearization approach called
the unscented transform which uses a set of deterministically
selected points that handles the nonlinearity. In UKF the
calculation of a matrix square root is required of the state error
covariance matrix, determines the spread of the sigma points
for the unscented transform. There are various ways that
calculate the matrix square root, which have been presented
and compared within GPS/INS application. GPS/INS are also
used for automobile applications such as autonomous
navigation,vehicle dynamics control, or sideslip, roll, and tire
cornering stiffness estimation.
A. INTEGRATION
OF GPS/INS/VISION SENSORS
TO NAVIGATE UNMANNED AERIAL VEHICLES
Integrated GPS/INS/Vision navigation system is used for
Unmanned Aerial Vehicles (UAVs). A CCD (ChargeCoupled
Device) video camera and laser rangefinder (LRF) based vision
system, combined with inertial sensors, provide the
information on the vertical and horizontal movements of the
UAV (helicopter) relative to the ground, which is critical for
the safety of UAV operations. Two Kalman filers has been
designed to operate separately to provide a reliable check on
the navigation solutions. When GPS signal is available, the
GPS measurements are used to update the error states in the
two Kalman filters, in order to estimate the INS sensors, LRF
and optic flow modelling errors, and provide redundant
navigation
solutions.Vision
system’s
the
corrected
measurements, the UAV’s relative movements relative to the
ground are then estimated continuously, even during GPS
signal blockages. The modelling strategy and the data fusion
procedure for this sensor integration scenario is discussed with
some numerical analysis results, demonstrating the potential
performance of the proposed triple integration.
B. DGPS/INS data fusion for land navigation
The interest in land navigation in increased for the recent years.
With the advent of the Global Position System (GPS) we have
now the ability to determine the absolute position anywhere on
the globe. The GPS system works well only in open
environments with no overhead obstructions and the un
avoidable errors occur when it there is obstruction.It is occured
frequently in urban environments, forests and tunnels. At least
four visible satellites are required in GPS Systems to maintain
a good position fix. In many situations in which higher level of
accuracy is required, the navigation cannot be achieved by
GPS alone.The design of a reliable multisensor fusion
algorithm uses GPS and Inertial Navigation System in order to
decrease the implementation cost of such systems on land
vehicles.
CONCLUSION
The paper has bought out some aspects of integrated inertial
navigation. We discussed about basics of global position
system and inertial navigation. Tightly coupled or ultra tightly
coupled scheme has features which individual systems do not
possess and is becoming the choice for aerospace high
dynamics area where performance and mission reliability are of
prime importance. Satellite navigation aiding is inertial systems
are integrated with SNS receivers whose cost strap down micro
inertial systems are integrated with the SNS receivers whose
cost has also come down over the years.
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International Journal of Technical Research and Applications e-ISSN: 2320-8163,
www.ijtra.com, Special Issue 42 (AMBALIKA) (March 2017), PP. 117-120
References
[1] Vincent Gabaglio, GPS/INS integration
for
pedestrian navigation. Lausanne, Switzerland, 2002.
[2] Vikas Kumar N, Integration of Inertial Navigation
System and Global Positioning System Using
Kalman Filtering. Mumbai, India, July 2004.
[3] Adrian Schumacher, Integration of a GPS aided
Strapdown Inertial Navigation System for Land
Vehicles. Stockholm, Sweden, March 2006.
[4] Tiziano Fiorenzani, C. Manes, G. Oriolo, P. Peliti
Comparative study of unscented Kalman filter and
Extended Kalman filter for position/attitude
estimation in unmanned aerial vehicles. IASR-CNR,
August 2008.
[5] Jakob Almqvist, INS measurements integration in a
GPS software receiver. Lule˚a University of
Technology, Department
of
Space
Science,
Kiruna, Sweden, 2009
[6] Yukihiro Kubo, J. Wang INS/GPS integration using
Gaussian sum particle filter. Ritsumeikan University,
Japan. University of New South Wales, Australia
[7] Klaus-Peter Schwarz, A. H. Mohamed Adaptive
Kalman Filtering for INS/GPS. Calgary, Canada.
December.
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