International Journal of Engineering Trends and Technology- Volume4Issue3- 2013
Design of a High Accurate Aircraft Ground-based
Landing System
Ahmad Abbas Al-Ameen Salih1,a and Amzari Zhahir2,b
1,2
Department of Aerospace Engineering, Faculty of Engineering, University Putra Malaysia
level is below the allowable limit or when pilots cannot see
Abstract
The rapid increase in aviation industry requires parallel
the runway. As it approach runway more accuracy is required
effective plans, programs and designs of systems and
since the limit for mismatching the touch point should not
facilities nationwide to fulfill the increasing needs for safe air
exceed meter level. Aircraft approach and landing are of the
transportation. Aircraft landing remains a problem for a long
most hazardous portions of flight. Accidents records indicate
time all over the world. Systems that aircraft rely on in
that approximately 50 percent of the accidents occur during
landing are unreliable to perform a precise guidance due to
aircraft landing (Lisrary & Afb, 2003). International Civil
many limitations such as inaccuracy, unreliability and
Aviation Organization (ICAO) has divided landing systems
dependency. In low visibility conditions, when pilots are
into three categories according to decision height, visibility
unable to see the runway, the aircrafts are diverted to another
and runway visual range. Category III C is not in operation
airport. However, low visibility can also affect all airports in
yet anywhere in the world because of systematic limitations
the vicinity, forcing aircrafts to land in low visibility
of landing systems in service. It requires landing with no
conditions depending on Instrument Flight Rules (IFR).
visibility or runway visual range. Currently, the limits of
Aircraft approach and landing are the most hazardous
integrity and accuracy of ground equipments have not been
portions of flight; accidents records indicate that
able to match ICAO standards and recommended practices.
approximately 50 percent of the accidents occur during
Nevertheless, they are still in use due to the lack of better
aircraft landing. Aircraft landing Category III C is not yet in
alternatives. The main current equipments limitations are:
operation anywhere in the world. It requires landing with no
inaccuracy, unreliability, vulnerability to multipath,
visibility or runway visual range.
obstruction in signal broadcasting, cause ground service
Currently, Global Positioning System (GPS) is the
cognition, lack of integrity and high cost.
main navigation system used all over the world for aircraft
In this paper, a ground-based positioning stations
navigation, approach and landing. However, in aircraft
based on concept of trilateration has been designed in order
approach and landing phase, the accuracy of GPS is not
to reduce or even to eliminate landing systems errors and to
sufficient to perform a perfect landing due to the possibility
achieve higher accuracy for landing of aircraft can meet CAT
of aircraft to be drifted out of the runway. The accuracy of
III C. system specifications have been calculated, designed
GPS could be improved to 3 meter by sending correction.
and simulated using Matlab. A simulated design has been
Improved accuracy has not been able to meet ICAO
performed using Matlab Simulink to simulate transmission
standards for aircraft automatic landing. In this paper, aircraft
and reception of data for accurate aircraft positioning and
landing systems characteristics, performance and accuracies
precise guidance to runway touch point. Positioning error
have been studied and compared for the purpose of assessing
sources have been considered and eliminated providing all
limitations and drawbacks. An aircraft landing system with
weathers high accurate aircraft landing system.
improved performance is proposed to meet ICAO standards
1.2.
Problem statement:
for all-weather aircraft landing required and recommended
The
level of accuracy for aircraft positioning has
practices with high accuracy to perform full automatic
been
achieved
has not been able to match ICAO standard for
landing for aircrafts.
CAT III C and it is not sufficient to fulfill aircraft automatic
Keywords: Landing System, Trilateration, Triangulation, Groundbased System, Accurate positioning, ILS, MLS, Positioning, GPS,
landing. ICAO favored GPS over MLS, however, GPS is not
and DGPS.
highly accurate and has many limitations make such system
not feasible to be used for aircraft automatic landing. GPS
1. INTRODUCTION:
accuracy could be improved by receiving differential
1.1.
Background:
correction messages (DGPS) to 3-5 meters. Hence, this error
The rapid increase in aviation industry needs parallel
may lead to drift aircraft out of runway and crash. Beside the
effective plans, programs and designs of landing systems and
lack of high accuracy, the other GPS limitations are: Satellite
facilities nationwide. Generally, in low visibility conditions,
unavailability, Satellite Geometry, Low vertical accuracy,
aircrafts are always diverted to another airport if the visibility
ISSN: 2231-5381
http://www.internationaljournalssrg.org
Page 415
International Journal of Engineering Trends and Technology- Volume4Issue3- 2013
Satellite signal broadcasting travel time is longer than signals
transmitted from ground surface, GPS receiver update rate is
low, Signal weakening and degradation, Ionospheric effects,
GPS lack of high accuracy. In order to overcome GPS
limitations, even though many systems have been designed to
augment GPS and improve the accuracy, no system can be
relied on to achieve a high accuracy in a range of less than 1
m for high speed applications with high integrity and
reliability. Table (1) compares between aircraft landing
systems accuracies.
Table 1: Aircraft landing systems accuracies:
Landing system
DME with ILS
DME/P
GPS
WAAS
DGPS
Accuracy (feet)
1200
100
30
25
10
2. Literature review:
Aircraft landing remains a problem for a long time all over
the world. Systems that aircraft rely on in landing are
unreliable to perform complete automatic landing due to
many limitations. As flying aircraft approaches runway, more
accuracy is required since the limit for mismatching the touch
point on the runway should not exceed meter level.
Commonly, aircrafts are diverted to alternate airport in low
visibility conditions when the visibility is below the
allowable limit. Until the mid-1950’s, only visual landing
procedures were possible. In 1958 the first Instrument Flight
Rule (IFR) landing system developed. Currently, the standard
radio landing guidance system used worldwide is the ILS (
Ackland et al., 2003) it was selected by (ICAO) in 1946 as
the international all-weather aircraft landing aid [3]. In order
to overcome the operational and technical problems of ILS,
ICAO has formulated guidelines for futuristic system that
will replace ILS. After evaluation the various systems,
ICAO has accepted Microwave Landing System (MLS) for
world-wide use [4]. Both ILS and MLS have many
limitations and they are not highly accurate relatively (Table
2). They are unable to provide navigation service for aircraft
flying in conditions of low visibility [5]. Hence, this is where
a GPS-based landing system has the potential to complement
landing systems, or even replacing them completely. Earlier,
several papers described about GPS-based precision approach
and landing [6–8]. The studies indicated that GPS was a
revolution never dreamed possible that has many advantages
over other navigation and landing systems.
Since the introduction of GPS, most existing MLS
systems have been turned off in North America. FAA
favored GPS over MLS [9]. The major issues with GPS,
guidance accuracy near the runway threshold and the
ISSN: 2231-5381
integrity of the system has not been able to match ICAO
standards practices. GPS integrity and availability was
enhanced by adding differential GPS (DGPS) to support new
applications, such as aircraft precision approach and precise
positioning. Therefore, the accuracy can be improved to
about 3 m. (Brown et al., 1996) performed flight tests to
examine DGPS as CAT III B. Results showed that accuracy
could be achieved are in meter level. (J. H. Rye et al, 2004)
used DGPS to increase the accuracy of GPS receiver for low
speed movement. The results showed that positioning errors
were considerably reduced. The maximum distance error was
0.546 m. As speed increases, accuracy decreases.
To improve GPS accuracy, many augmentation
systems have been used such as the Differential GPS, Wide
Area Augmentation System (WAAS) and Local Area
Augmentation System (LAAS). (Lawrence et al., 1996)
designed integrated system of Wide Area DGPS with local
Area Kinematic DGPS to improve accuracy. Results showed
that messages were lost and real time correction messages
were disappointing. [11] studied Real-time GPS navigation
accuracy during approach and landing of ultra-light aircraft
using simulated LAAS. The study indicated that accuracy is
improved from 4.57m to 3.12m in dynamic tests.
Stanford University has developed the Integrity
Beacon as a means of augmenting GPS to provide the
performance required to achieve the specifications of
Category III. Results showed that, all the touchdown points
are within this 95 percent touchdown box [12]. FAA has
established an evaluation program to test the technical
feasibility of using DGPS based technology for CAT IIIB
precision approach and landing applications. Results
indicated that, all of the touchdowns were accomplished with
the outboard landing gear position less than 145 ft away from
the runway centerline [13]. However, the error of 145 ft is
not acceptable especially in low visibility conditions.
In 2012, FAA has published Next Generation
Implementation Plan (“Next Generation GPS Operational
Control Segment,” 2012). FAA plan to use Ground Base
Augmentation System (GBAS) for civil aviation local
augmentation to support all flight phases including aircraft
approach and landing. In 2011, a contract was awarded to
produce Category II and III LAAS ground facility prototype.
The plan expected capitalizing on satellite technology to
implement landing procedures during periods of low
visibility. By 2012, aircraft can land in low-visibility
conditions. In 2012, at Bremen Airport, DFS Deutsche
Flugsicherung was the first air navigation service provider in
the world to operate GBAS for CAT I precision approaches
for regular air services (“Satellite-based landing system
certified”, 2012.). By the middle of this decade, certification
for GBAS operations under all-weather operations CAT II
and CAT III is expected.
http://www.internationaljournalssrg.org
Page 416
International Journal of Engineering Trends and Technology- Volume4Issue3- 2013
The use of GPS-based system for aircraft landing
did not satisfy researchers and operators as well and the
results have proved the lack of reliability and inaccuracy of
the system (Mitelman, 2004; Lawrence et al., 1996; David et
al., 1995; B. Pervan et al., 1997). Landing CAT III C is not
in operation yet anywhere in the world due to unreliability,
inaccuracy and dependence of used systems. Table 2
compares between aircraft landing systems accuracies. In this
study, an autonomous aircraft landing system will be
designed to overcome GPS limitations and provide a better
alternative high accurate landing system.
Figure (1): Ground-based aircraft landing system transmitters
3. Aircraft Landing System:
The civil aviation industry is developing rapidly to occupy
the increasing needs for faster, comfortable and safe
transportation. Aircraft landing is a critical phase and high
accuracy in required especially when flying under low
visibility conditions. The zero accident policy announced by
FAA requires airliners to have essentially perfect navigation
from take-off to landing (Aviation Safety Action Plan, 1995).
ICAO has divided landing systems into three categories
according to decision height, visibility and runway visual
range [18]. Category IIIC operation requires precision
instrument approach and landing with no decision height and
no runway visual range limitations.
3.1. Aircraft Ground-based Landing System:
A perfect navigation in landing phase needs a high accuracy
to enhance safe aircraft landing in all-weather situations.
Currently, no system has the capability to achieve aircraft
landing CAT III C which enables the aircraft to land in allweather conditions and when the visibility level is low. In
this paper, a high accurate ground-based aircraft landing
system specifications will be designed to overcome previous
aircraft landing systems limitations and to achieve high
accurate guidance for aircrafts with improved capabilities and
performance to meet ICAO CAT IIIC.
3.1. System components:
 4 signal transmitter.
 Signal receiver on aircraft with 4 channels.
 5 clocks; one in each transmitter (4 transmitters),
and one in receiver.
The figure below shows the system components and the
distribution of transmitters’ towers around the runway.
ISSN: 2231-5381
3.2. System theory of operation:
This system is based on a simple mathematical principle
called Trilateration. Four base stations surveyed and located
precisely beside the runway are used to broadcast radio signal
to aircraft’s receiver (figure 4.1). The system is totally
autonomous. It broadcasts its own signals in specific
frequencies via 4 channels. In aircraft landing positioning, 3
dimensions are required (longitude, latitude and altitude).
The use of 3 transmitters provides a positioning with 2
dimensions (latitude and longitude) while 4 transmitters
provide a full positioning with 3 dimensions since altitude is
significantly needed for aircraft landing system with high
accuracy.
To locate itself, a receiver must find the distance to four
transmitters of known position. If the receiver finds the
distance from one transmitter, it knows that it must be
somewhere on an imaginary sphere, with the transmitter as
the center a radius of calculated distance between transmitter
and receiver. If the receiver can generate spheres for two
transmitters, it knows it can only be located in the surfaces
intersection of the two spheres. The two spheres overlap in a
ring of possible receiver positions. By generating a sphere for
a third transmitter, the receiver narrows its possible position
down to two points. When the coordination is performed
using three transmitters, the receiver dismisses the point
located in space leaving only one possible position assuming
that the receiver is at mean sea level. By using the fourth
transmitter, altitude can be determined where the fourth
sphere intersects with in one of the two points.
3.3. Aircraft position calculation:
A receiver on the aircraft receives the transmitted radio
signals from ground stations transmitters and measures the
time delay that the signal takes between transmission and
reception. Both transmitters and receiver have a precise
clock. The signal transmitted contains information about
signal transmission time, so the receiver uses its clock to
compare time of transmission in the transmitted code with
time of reception to calculate time difference.
http://www.internationaljournalssrg.org
Page 417
International Journal of Engineering Trends and Technology- Volume4Issue3- 2013
Clocks are synchronized between receiver and transmitter. As
receiver receives signal containing time code, it generates its
time code internally and uses it to compare between two
codes. The receiver determines the range between aircraft
and each one of the four stations (figure 2).
Range = (speed) . (time)
(1)
Where the speed of the signal is the speed of light which
travels at 299 792 458 m / s and time is the time that the
signal takes between transmitter and receiver. The receiver
then calculates the coordinates (latitude, longitude and
altitude) of the aircraft depending on the ranges to the four
known reference stations by using positioning equations.
Equation (2), (3), (4), and (5).
Figure (2): Time difference calculation
3.4. Positioning equations:
Equations of Pseudorange are used to calculate distance to
each signal transmitter. The four ranges are used to calculate
the accurate position of aircrafts.
ρ1= √ (x1 – X)2 +(y1 – Y)2 +(z1 – Z)2
ρ2= √ (x2 - X)2 +(y2 - Y)2 +(z2 - Z)2
ρ3= √ (x3 - X)2 +(y3 - Y)2 +(z3 - Z)2
ρ4= √ (x4 - X)2 +(y4 - Y)2 +(z4 - Z)2
(2)
(3)
(4)
(5)
Where X,Y,Z are the coordinates of ground station and
xn,yn,zn are the coordinates of aircraft.
3.5. Receiver equations solutions:
Aircraft receiver solves the 4 equations of ranges from 4
stations transmitters simultaneously to calculate the position
of the aircraft accurately. Since the locations of the
transmitting stations are known, they can be used as a
reference points to calculate aircraft position. All ranges to
stations are calculated from time difference of signal
transmission and reception. These values are used by receiver
in pseudorange equation to calculate the position. The four
equations derived from the four stations are used to find out
the values of (x,y,z) of the aircraft.
3.6. System advantages:
This system is proposed to overcome the majority of aircraft
landing systems limitations. It has many advantages over
current systems. The main purpose of this study is to design a
system to reduce some positioning errors and eliminate
ISSN: 2231-5381
others. This study aims to meet ICAO standard for CAT III C
which gives aircraft the ability to land in low visibility
conditions and even when the visibility does not exist at all
and there is no runway visual range.
Compared with the use of GPS for aircraft landing, Aircraft
Ground-based Landing System provides solutions for many
GPS error sources; the ionosphere and troposphere causes the
largest error for GPS signal. Ionospheric and tropospheric
errors considerably could be reduced because signal is
transmitted from earth surface and does not travel through
these layers. This will put troposphere and ionosphere out of
the equation.
In addition, this system gives the real and accurate altitude of
the aircraft since it refers to the real height of the runway, not
the mean sea level nor the earth ellipsoid like GPS.
Moreover, the signal broadcasted from satellites takes about
0.07 second to reach to earth whereas it takes about 0.000004
second if the signal is transmitted from earth surface. Beside
that, signal transmitted from Ground-based system will be
stronger. It can penetrate construction in vicinity of airport.
Additionally, satellites unavailability due to satellites
distribution or construction blockage is a serious problem in
critical stages of landing, this system is designed to be
available continuously within the approach and landing area.
Also, due to the distribution of satellites the vertical accuracy
is always less than horizontal accuracy. More than that it
causes an accuracy reduction when the visible satellites are
all clustered together in a single quadrant, this narrows
satellites visibility angle and consequently reduce the
positioning accuracy. In this system, transmitters stations are
distributed is precisely surveyed location with different
towers height to give a wide visibility angle and provide
accurate altitude (figure 1). Furthermore, this system is
completely autonomous. It does not depend on GPS satellites
such as DGPS where GPS errors are inherited and involved
in calculation, nor any other system. Finally, no need for
sending differential correction messages from DGPS stations.
This will eliminate data link problems and errors.
3.7. System specifications calculation:
Signal transmitted plays the major rule in the whole operation
of accurate positioning of aircraft and enhances to improve
the safety of landing automatically. A small signal problem
could lead to disaster due to sensitivity of stage.
4.7.1. Covered area:
Normally, in Instrument Landing System the Outer Marker
(OM) beacon is located at 7.4 to 13 kilometers from the ILS
threshold to mark the point at which glide slope altitude is
verified or at which the aircraft descent (“Terminal Area
Separation Standards : Historical Development”, 1997). The
first signal that aircraft receives from ILS is from outer
marker when it is about 7-13 km from runway threshold.
http://www.internationaljournalssrg.org
Page 418
International Journal of Engineering Trends and Technology- Volume4Issue3- 2013
Aircraft Ground- based Landing System is designed to
transmit signal in a range of 13 km from runway threshold
for aircraft approaching and landing.
3.7.2. Earth curvature effect:
Earth has a curvature at the approximate rate of 6 feet
for every 9 miles [20]. In this study, the distance is
considered small relatively since the system is used
particularly for aircraft approach and landing so the effect of
earth curvature is neglected. The curvature of the earth
affects signal transmission only over a long distance (Figure
3).
Figure (3): Earth curvature effects over long distance.
3.7.3. Distance between transmitters:
A distance between transmitters is a very important factor
must be taken into consideration in aircraft landing system
design. The precisely calculated distribution of towers around
the runway provides efficient operation with the best
performance. Figure (4) indicates transmitters distribution
around the runway. As transmitters are separated apart, the
value of PDOP increases providing a better availability and
more accurate positioning. Moreover, the vertical accuracy
will be extremely improved. Overall, the possibility of signal
to overlap will be less.
Frequency (VHF) band could be used to cover the required
area for aircraft approaching and landing.
The chosen frequency should be in a range where the signal
propagation is not influenced by weather phenomena like,
rain, snow or clouds. The characteristics of
VHF propagation are ideal for short distance terrestrial
transmission. VHF radio does not reflected by the ionosphere
and thus transmissions are restricted to the local area. It does
not interfere with transmissions thousands of kilometers
away. Therefore, it is less affected by atmospheric noise and
interference from electrical equipment than lower
frequencies. Whilst it is easier than HF and lower frequencies
to be blocked by land features, it is less affected by buildings
and other less substantial objects than higher frequencies.
Certain subparts of the VHF band have the same use around
the world. Frequency range from 108 to 118 MHz is used for
Air navigation beacons VOR and ILS [21]. In this system,
data are broadcasted to receiver via four different channels in
frequencies (110 MHz, 112 MHz, 114 MHz and 116 MHz).
3.7.5. Wavelength:
λ=v/f
(6)
In this equation v is speed of light. For VHF range the wave
length is between 1-10 meters. Wavelengths for system
frequencies are listed in table (2).
Table (2): system channels frequencies wavelengths:
Frequency
(MHz)
110
112
114
116
Wavelength
(m)
2.727
2.679
2.632
2.586
3.7.6. Doppler shift:
Doppler shift is the change in wave frequency and
wavelength of observer due to relative movement between
observer and wave source. Scientifically, when the relative
speeds of source and receiver to a medium are lower than the
wave velocity in the medium, received frequency
Figure (4): the distribution of transmitters around the runway
The distance for each of front transmitters from runway
center line is 1 km and for the back transmitters it is 1.5km.
Distance between front transmitters is 2 km and between
back transmitters is 3 km. Distance to runway touch point for
front transmitter is 1 km and for back transmitters is 3.354
km.
3.7.4. Frequency:
The travelled signal range depends on frequency of the
signal. This system is proposed to be used for aircraft landing
where the area is considered small relatively, so a very High
ISSN: 2231-5381
and
emitter frequency
could be calculated from the formula:
Change in frequency:
Δf = ( Δv / c) fo
(7)
Where: c is the velocity of light, V r is receiver velocity and
Vs is source velocity.
The frequency change in approaching aircraft receiver due to
the relative movement between transmitters and aircraft
receiver could be determined as follows:
For aircraft landing with speed of 100 km/h when source
frequency is 110 MHz:
Doppler shift = 36,666.67 HZ = 0.03667 MHz
http://www.internationaljournalssrg.org
Page 419
International Journal of Engineering Trends and Technology- Volume4Issue3- 2013
Frequency shift is proportional to aircraft speed and also to
transmitter frequency.
3.7.7. Transmitter power:
The general rule of transmitter power is it will take four times
the power to double the transmission distance. Transmission
range could be increased by increasing antenna height
without increasing power. Raise the height significantly
increase broadcast distance. Typically, transmission power is
measured in dBm. The greater transmission power, the
greater distances can be achieved. Friis transmission equation
(equation 4.15) is used to calculate transmitted and received
power ratio (Pr/Pt). Whereas, equation 10 is used to calculate
the power received.
Pr / Pt = Gt Gr (λ /4 Π R)2
(8)
where Gt and Gr are transmitter and receiver antennas
gains respectively, Pt and Pr are transmitted and received
power respectively, λ is the wavelength, and R is the
distance.
A typical VHF station operates at about 100,000 watts (80
dBm). Transmitter power = 100 KW (100,000 W).
Transmitter power in dB = 10 log 100,000 = 50 dBW =80
dBm
Figure (5): The height of front and back transmitters
3.7.10. Antenna gain: it is a unitless measure that combines
antenna’s efficiency (Eantenna) and directivity (D):
G = Eantenna . D
(13)
In aviation VHF transmission, experiments and theoretical
formula comparison showed that it is a good approximation
for a general model to use the maximum gain of transmitter
and receiver; respectively, they are -4 dB and 2.15 dB (
Roturier & Chateau, 1999; Maschinenbau, 2011).
3.7.11. Path loss:
Free-space path loss is proportional to the distance squared
between the transmitter and receiver, and also proportional to
the radio signal frequency squared. The equation for FSPL is:
FSPL = (4
3.7.8. Received power:
Power received in dB:
Pr=Pt(dB)+Gt(dB)+Gr(dB) - 20log(4 d/λ)
(9)
= - 43.5 dBW = 0.000,0447 W = -13 dBm
3.7.9. The height of the antennas:
The height of the antenna is the most important factor to
consider. It is used to calculate covered area. The area
covered could be calculated from the formula:
Distance (km) = √12.746 × Am
(10)
Where Am is the height of the antenna in meter. For front
transmitters, the coverage area is about 13 km. so,
13= √12.746 × Am
(11)
Am= 13.259 m
For the two back transmitters, the covered distance includes
the length of the runway. For large aircrafts, the runway is
designed with a length of 3 km. This means for two back
transmitters the covered distance must be taller to cover
approximately 16 km (Figure 5), hence:
16 = √12.746 × Am
(12)
Am = 20.085 m
Transmitter antenna radiates radio wave uniformly and
continuously in all directions. Omni-directional antenna is
used for transmission and reception of signal.
= (4
d / λ)2
(14)
d f / c)2
Table (3) and Table (4) shows the FSPL for front and back
transmitters.
Table (3): Free Space Path Loss (FSPL) when range is 13km for different
frequencies:
Frequency (MHz) Wavelength (m) FSPL (dB)
110
2.727
95.55
112
2.679
95.7
114
2.632
95.86
116
2.586
96.01
Table (4.4) determines the level of FSPL when the covered
range is 16 km.
Table (4): Free Space Path Loss (FSPL) when range is 16km for different
frequencies:
Frequency (MHz)
110
112
114
116
Wavelength (m)
2.727
2.679
2.632
2.586
FSPL (dB)
97.35
97.51
97.66
97.81
In Figure (6), curves indicate the path loss in free space for
150 MHz and 200 MHz. it can be observed that, path is
directly proportional to signal frequency and also to distance
between transmitter and receiver.
ISSN: 2231-5381
http://www.internationaljournalssrg.org
Page 420
International Journal of Engineering Trends and Technology- Volume4Issue3- 2013
antennas to be directed to each other because it radiates radio
waves equally and uniformly in all directions.
Figure (6): the path loss in free space for 150 MHz and 200 MHz.
3.7.12. Aircraft approaching and landing:
The distance from the runway where the aircraft starts to
descend differs for airports. Therefore, the best glide speed
and the glide ratio depend on the aircraft. Normal descents
take place at a constant airspeed and constant angle of
descent (3-4 degree final approach at most airports) [24]. In
this system altitude determination is referenced to the height
of the runway.
3.7.14. System coordination:
To indicate an object position precisely, many systems have
been developed for this purpose such as Decimal degrees. As
with latitude and longitude, the values are bounded by ±90°
and ±180° respectively. Typically, latitudes are mentioned
before longitude. The other system used for coordination is
UTM where coordinates are expressed as a distance in meters
to the east and a distance in meters to the north. In UTM
system coordinates are expressed in meters. In this system, an
approaching aircraft positioning has been simulated using
UTM system providing the transmitters heights and
coordinates with respect to runway. Figure (8). Towers have
been located around the runway according to calculations
have been made determining transmitters height and
locations.
Figure (7): Aircraft altitude, distance to touch point and angle of decent
At a distance of 13km from runway touch point with a
descend angle of 4°:
cos 4 = 13/h
(15)
h= 13.0178
Sin 3 = altitude/h
(16)
Altitude= 0.909 km = 909 m
The determination of altitude according to the descend angle
and distance to touch point are summarized in (Table 5):
Figure (8): transmitters coordinates around the runway
Table (5): aircraft altitude for 4 degree descend angle:
Distance to touch point (km)
13
8
5
3.354
3
1
0.1
Aircraft altitude (km)
0.909
0.559
0.350
0.235
0.210
0.070
0.007
The angle between transmitter aircraft receiver:
Calculation done showed that, for aircraft landing with a
maximum angle of decent of 4°, antennas angle are: θ = 3.93°
for front transmitter and θ = 3.166° for back transmitters.
However, the use of omni-directional antenna does not need
ISSN: 2231-5381
As can be seen in the figure, transmitter coordinates are (0, 0,
20.085), (500, 3000, 13.2599), (2500, 3000, 13.259), (3000,
0, 20.085). The z values indicate the height of transmitter
antenna.
3.7.15. Bad weather effect:
Landing of aircrafts in a bad weather condition when there is
no visibility requires a perfect positioning with high
reliability and error possibility in a range not more than 1 m.
currently, there is no landing system has this capability all
over the world. Beside causing visibility reduction, bad
weather affects the signals transmitted to aircraft which
means signal delay needs significantly to be taken into
account because an error in a signal of 1/100 second would
http://www.internationaljournalssrg.org
Page 421
International Journal of Engineering Trends and Technology- Volume4Issue3- 2013
lead to an error in the position determination of about
3,000 km.
Generally, weather radar data is used as an indicator of
troposphere delay differences between two locations. Radar
data of reflectivity is a good source to determine the effects
due to weather condition, rain rate and suspended water
droplets. The impact of these delay differences was found to
be less significant and has no effect over signal travel time.
Studies showed that the effect of rain could be neglected in
signal propagation especially in low frequency and over short
ranges of transmission.
Researches in GPS indicated that, rain, fog, snow, dust have
no effect on GPS signal, and that is why GPS is considered as
all-weather system. More accurate other GPS studies have
shown that troposphere delay is increased due to the presence
of severe weather fronts and heavy rain. (Gregorius &
Blewitt, 1998) showed that troposphere zenith delay can
increase up to 8 cm when a warm weather front approaches
the receiver. Another study showed the significance of
various tropospheric components on GPS signal accuracy is
(Solheim et al., 1999). It has shown that water vapor, cloud
liquid, rain and sandstorms can induce significant delays.
According to the information provided in (Solheim et al.,
1999), the delay induced due to water vapor is large
compared to various other atmospheric components and can
reach up to 140 mm/km for vapor diameter less than 10-7
mm. On the other hand, delays induced by clouds are less
than 8 mm/km and drizzle and steady rain can induce surface
delays of 0.2 mm/km and 2 mm/km, respectively, Also, it is
reported in (Solheim et al., 1999) that water vapor has the
largest contribution in the wet delay. The fog is considered as
another form of rain. The importance of attenuation caused
by fog is minor and could be neglected at frequencies lower
than 2 GHz [27]. Scientists assume that, snow attenuation is
less than rain attenuation falling at the same rate. Radio
waves attenuation caused by hailstones is considerably less
than that caused by rain. Figure indicates that in a heavy rain
(200 mm/hour) the distance error is about 20 mm/km
(Solheim et al., 1999).
Another researches about VHF ground transmitters
propagation effect in bad weather condition found that, signal
is not affected by the presence of rain as it is similar to free
space propagation. The analysis of the radar backscatter
measured signal delay in different rainfall rates does not
show organized and salient time delays ( Roturier & Chateau,
1999).
3.7.16. System multipath:
Previously, many researches have been done intending to
mitigate the effect of signal multipath. In GPS positioning, it
is one of the major sources of position error. However, many
techniques have been produced to reduce and even eliminate
the phenomenon. There are a wide variety of mitigation
techniques which employ schemes of data processing.
Progress in Electromagnetics research measurements provide
an efficient reduction of the multipath to centimeter level and
are widely used. Other typical methods are focusing on
taking advantage of SNR measurements, repeatability of
multipath at ground reference stations. Multiple receivers can
be used to cancel spatial correlated multipath. The results due
to adaptive filtering methods are encouraging and significant
reduction of error to centimeter level is observed. A choke
ring antenna is originally designed to mitigate multipath.
Many studies compared between different types of antennas,
results showed that the choke ring antenna has the best
performance in mitigating multipath.
A more specialized study about the use of VHF for
aircraft transmission has been conducted dedicating to
introduce a general model for fading on the aeronautical VHF
multipath channel ( Roturier & Chateau, 1999). The model
designed is based on previous theoretical and experimental
multipath studies developed in the context of VHF Digital
Link (VDL) system validation. Practically, determining
receiver and transmitter antennas radiation prosperity is the
main challenge, however, experiments and theoretical
formula comparison presented in ( Roturier & Chateau, 1999)
showed that it is a good approximation for a general model to
use the axisymmetric radiation diagram functions of a
vertical half-wavelength dipole and maximum gain Gmax of
transmitter and receiver such as defined in [23], respectively,
they are:
20 log 10 (max ground) = -4 dBi
(18)
20 log 10 (max ground) = 2.15 dBi
(19)
4.
Figure (9): The effect of rain in signal delay over distance
ISSN: 2231-5381
Aircraft Ground-based Landing System
simulation:
In previous section, Aircraft Ground-based Landing System
characteristics and specifications have been calculated to
enable the system to precisely locate the aircraft position and
enhance it to approach and land safely. In this section, system
specifications will be simulated to test the system
performance and evaluate the positioning accuracy. This
http://www.internationaljournalssrg.org
Page 422
International Journal of Engineering Trends and Technology- Volume4Issue3- 2013
system will be simulated using Matlab Simulink. It provides
built-in support for prototyping, testing, and running models
on low-cost target hardware. It provides the possibility of
comparing theoretical results with experimental results.
4.1. Simulation design:
The operation of broadcasting data from transmitters to
receiver takes place in sequent steps start by generating of
signals and codes (0’s and 1’s) to be decoded. Each one of
the four transmitters has its unique code which is used by
receiver to identify transmitters individually. After that signal
is modulated and broadcasted through channel. All signals
are received by one receiver in aircraft. Signal are
demodulated, decoded and then displayed. Code received is
used to determine transmitters’ locations and distance to each
one of them. Figure (10) shows the process of data
transmission and reception.
Figure (10): Aircraft Landing Ground-based System simulation blocks
4.2. One transmitter simulation:
Data transmission takes place from each transmitter to
receiver individually. One Transmitter/Receiver circuit
(Figure 11) is used to examine time delay,
transmitter/receiver error correlation and multipath effects.
Figure (11): Data transmission from one transmitter to receiver
ISSN: 2231-5381
http://www.internationaljournalssrg.org
Page 423
International Journal of Engineering Trends and Technology- Volume4Issue3- 2013
equations and locate aircraft. A very small clock drift leads to
remarkable position error. Matlab time scope block shows
time difference precisely.
4.3. Time delay:
The broadcasted signal contains a code generated by
transmitters. Broadcasted signal includes: The time of
message transmission and transmitter position when message
is transmitted. Receiver receives the signal and generates
internal code which is compared with transmitted code to
determine lag time to each transmitter since each one has its
unique code. Figure (11) shows transmission operation
simulation. (Figures 12.a and 12.b) show the signal pulse
generated in transmitter and receiver.
4.4. Attenuation and Multipath:
Rayleigh and Rician fading channels are useful models of
real-world phenomena in wireless transmission. These
phenomena include multipath scattering effects, time
dispersion, and Doppler shifts that arise from relative motion
between the transmitter and receiver (Loo & Secord, 1991).
The Communications System Toolbox provides a plotting
function that helps to visualize the characteristics of a fading
channel. For direct line-of-sight path from transmitter to
receiver Rician Fading Channel is used while for one or more
reflected paths from transmitter to receiver Multipath
Rayleigh Fading Channel is used.
Figure (12.a): Transmitted signal pulse
Figure (14): Rayleigh fading channel multipath
Figure (15) shows Rician fading channel multipath. Relative
motion between the transmitter and receiver causes Doppler
shifts in the signal frequency (Figure 16).
Figure (12.b): Received signal pulse
Time difference between transmitter and receiver specifies
the distance that the signal takes to reach to receiver (Figure
13). Time differences provide a solution for positioning
equations to locate the aircraft.
Figure (15): Rician fading channel multipath
Figure (13): Time difference between transmission and reception
Determination of distance between transmitter and receiver is
carried out using the received code since receiver and
transmitters’ clocks are precisely synchronized. Distance is
continuously computed by receiver to solve trilateration
ISSN: 2231-5381
http://www.internationaljournalssrg.org
Figure (16): Doppler spectrum
Page 424
International Journal of Engineering Trends and Technology- Volume4Issue3- 2013
The Doppler spectrum is a statistical characterization of the
fading process. The channel visualization tool makes
periodic measurements of the Doppler spectrum (blue dots).
The Multipath Rician Fading Channel block implements a
baseband simulation of a multipath Rician fading
propagation channel (figure 15). This block is used to model
wireless transmission systems when the signal travels along a
line-of-sight or direct path (Tsai, 1994).
Multipath simulation results showed that the
analytical results match with GPS and VHF transmission
systems results such as in (Hannah, 2001; Roturier &
Chateau, 1999; Hoeher, Haas, & Kiel, 1999; Hajj & Young,
2002; Rost & Wanninger, 2012). Multipath is directly varies
from one transmission environment to another. The number
of signal reflected is different changes as the aircraft moves.
The corresponding numerical results have been presented has
shown that the analytical and simulation results match quite
well for both static and dynamic environments. Since these
analytical results are optimal among standard transmission
systems, they can be applied to analyze the performance real
aircraft landing system despite of that multipath effects
depend on transmission environment and number of reflected
paths and this could be different from one airport to another.
Nevertheless, it is easily can be modeled and mitigated.
4.5. Transmitters positioning system simulation:
As in GPS, in order to determine the aircraft coordinates, at
least, a signal from different four transmitters is required. In
this system simulation, trilateration positioning equations
have been solved using Matlab. Four transmitters’
coordinates and distance to each one of them are required to
determine receiver location coordinates. Matlab simulation
showed that distance from three transmitters assumes altitude
is on earth surface so a signal from four transmitters at least
is required. Figure (17) shows two possibilities of altitude for
ranges from 3 transmitters.
Figure (17) : three transmitters, two possible altitudes.
4.6. Aircraft accurate positioning simulation:
Since transmitters are in the same area and they are close to
each other relatively, environmental conditions affect
ISSN: 2231-5381
transmitters equally. Initially, to simplify the explanation of
accurate positioning process, an imaginary system has been
established. Matlab code (figure 18) has been used to
determine aircraft coordinates (x,y,z).
Figure (18): Matlab aircraft positioning code
4.7. High accurate Ground-based Aircraft Landing
System position calculation error:
Figure (19) indicates the positions on transmitter’s towers.
Figure (19): transmitters towers positions
Simulation results showed that, when system has an error of
20 mm/km from transmitters, the system is feasible; the
maximum position error is 4 m. When simulating a landing
system using the same characteristics with error of 1mm/km,
the position errors determined in three dimensions does not
exceed 0.2062 m.
Aircraft position has been calculated and simulated taking
into account the position error. Positing errors are the
differences between route coordinates and aircraft position.
The route points coordinates have been calculated according
to distance to aircraft runway touch point and altitude when
the aircraft descending with an angle of 4 degrees. Figure
(20) shows the aircraft approaching and landing to runway
touch point. The aircraft appears as a red dot rounded by a
circle. The dot in the center indicates the route data point or
the accurate aircraft position as there is no position error. The
circle rounded the dot indicates the positioning error since
aircraft could be at any point in the circumference. The
position error identifies the circle radius.
http://www.internationaljournalssrg.org
Page 425
International Journal of Engineering Trends and Technology- Volume4Issue3- 2013
Figure (20): Aircraft route position and error limits
Generally, the main positioning error factors are: ionospheric
and tropospheric delays, signal multipath, receiver clock drift
and receiver noise. In order to achieve an accurate aircraft
positioning, accuracy reduction factors must be eliminated. In
this system, weather conditions have no effect due to the use
of VHF band and also because signal traveled distance is
short relatively. The uses of modern techniques reduce
multipath effect to minimum. Researches indicated multipath
positioning accuracy reduction is in centimeter level.
Receiver clock drift is corrected by receiving signal from
many separated transmitters clocks. Receiver noise and
receiver malfunctions errors have been reduced using a good
performance and high reliability.
The number and the strength of reflected signals depend on
transmission environment. Signal reflections increase as
the distance between the transmitter and a receiver decreases.
As aircraft approaches, the signal multipath effect increases.
The technology of Trimble’s Everest multipath rejection
provided a high-accuracy solution for positioning
applications. Everest GPS Pathfinder provides up to 50%
higher accuracy than previous systems since multipath
signals are rejected. Another test results from RT2 real-time
positioning system developed by NovAtel indicated the level
of multipath effect is considerably reduced. Dynamically, the
error is 13.3 cm horizontally and 15 cm vertically. Table
(5.8) simulates approaching aircraft positioning with an effect
of multipath of 13.3 cm horizontally and 15 cm vertically.
The reflection of signal depends on the environment of signal
transmission and reception which is totally different from one
place to another, as a consequence, a multipath effect is
continuously changing as aircraft approaches. Signal
multipath mitigation depends on antenna and receiver design.
In this system, a receiver is expected to have a high
performance and ability to mitigate multipath to low limits.
A receiver noise is another source of error that causes an
accuracy reduction. However, modern and advanced
techniques using integrated hardware and improved
algorithms reduces this factor to low levels and even it could
be neglected. [34] conducted a research to assess GPS
receiver noise effect. The precision achieved is at the
millimeter level. Studies showed that even for high accurate
positioning, receiver noise can be neglected.
Table (7): Aircraft positioning with multipath effect of 13.3 cm horizontally and 15 cm vertically
Distance to touch
Route coordinates
point (km)
(x,y,z)
13
(1500, 16000, 909)
8
(1500, 11000, 559)
5
(1500, 8000, 350)
3.354
(1500, 6354, 235)
3
(1500, 6000, 210)
1
(1500, 4000, 70)
Figure (21) shows the relationship between positioning
accuracy and distance to runway touch point. As the aircraft
approaches, the effect of multipath increases and
consequently the accuracy is decreased.
Aircraft position
(x,y,z)
(1500.001, 16000.002, 909.02)
(1500.02, 11000.05, 559.08)
(1500.04, 8000.07, 350.11)
(1500.05, 6354.09, 235.126)
(1500.06, 6000.1, 210.13)
(1500.087, 4000.1, 70.15)
Position error
(m)
0.020
0.096
0.136
0.163
0.175
0.200
Figure (21): Positioning accuracy as aircraft approaches
ISSN: 2231-5381
http://www.internationaljournalssrg.org
Page 426
International Journal of Engineering Trends and Technology- Volume4Issue3- 2013
4.8. Ground-based Aircraft Landing System Indicator
simulation:
ILS indicator simulator has been designed using
VisualBasic.net to simulate data reception and displaying. As
the receiver receives the signal from ground-based
transmitters, it determines its current location which is
updated continuously. Since the main purpose of this system
is enhancing the aircraft to land with a high accuracy
positioning, aircraft drift from route is indicated precisely.
Vertical and horizontal deviations have been displayed in
ILS-style display which has been attached for an easier
indication of the aircraft position with respect to route data.
The vertical deviation has been determined based on the
difference in altitude between determined position and route
data. The horizontal deviation has been calculated using
azimuth between two points.
Route data are recorded in simulator. As a particular route is
chosen, all data regarding destination will be presented
including distance and time to destination and route drift data
as well. System compares between positioning data and route
data to determine position deviation. As system detect any
drift, landing indicator display the amount of deviation. The
deviation could be either in horizontal or vertical
coordination or in both of them. The system may be
connected to auto-pilot to follow the route data precisely and
land the aircraft automatically. The system determines the
true altitude of the aircraft above the runway unlike GPS
altitude determination which is based on altitude above mean
sea level not above runway. The simulator indicates current
altitude, route altitude and difference between them. As the
aircraft fly above route recommended altitude, the indicator
will be under the center and pilot must decent until indicator
point to center, and vice versa.
Figure (23) explains the changes of ILS indicator as the
aircraft approaches. In point A, aircraft is in left of runway
centerline. Pilot must turn right. In the same point, the
aircraft is lower than recommended landing path. Pilot must
go up. In point B, aircraft is heading into correct coordinates.
The indicator shows the improvement of lateral and vertical
indication. As the aircraft reaches point C, where it is the
correct coordinates, indicator deviation vanished.
Figure (23): ILS indicator deviation
Touch point coordinates (x,y) are (1500, 3000) in UTM
system. When it is converted to decimal degrees, it is
equivalent to (-175.475306, 0.0270586283). The simulation
showed that the azimuth between the two points (1500, 3000)
and aircraft coordinates (1500, 16000) is 360°. The aircraft is
in a straight light with runway centerline. When comparing
the two points: runway touch point is (1500, 3000) and
aircraft position is in point (1600, 16000), the azimuth
reading between the two points is 0.431°. The runway center
line in on the right to pilot; pilot must turn right. Figure
(23.a). When comparing the two points: runway touch point
coordinates: (1500, 3000) and aircraft position (1400,
16000), the azimuth reading is 359.55°. The runway center
line in on the left to pilot; pilot must turn left. Figure (23.b).
4.8.1. ILS indicator:
Tepically, in ILS, two independent indicators are used to
guide the aircraft laterally and vertically. In order to correct
position error, the pilot needs to center the two indicators; left
and right for lateral indicator, up and down for vertical
indicator. Figure (22).
(a)
(b)
Figure (5.23): ILS indicator
Figure (24) shows the aircraft landing system display.
Figure (22): ILS indicator
ISSN: 2231-5381
http://www.internationaljournalssrg.org
Page 427
International Journal of Engineering Trends and Technology- Volume4Issue3- 2013
Figure (24): Aircraft landing system indicators
5. Conclusion:
Aircraft landing is a very critical stage. The risk for aircraft to
be drifted out of the runway or crash building or other aircraft
is high so a superior accuracy is required to guide aircraft to
runway touchdown point precisely. In bad weather conditions
when visibility is low or runway visual range does not exist,
aircraft rely on full automatic system to land systematically.
Currently, no system is able to provide this reliability all over
the world. In this study a new landing system has been
proposed to reduce and eliminate many aircraft landing
systems limitations. System characteristics and specifications
have been calculated to enhance aircraft to land in all
weathers safely with high accuracy guidance.
Aircraft landing ground-based system provides solutions for
many landing systems problems and reduces some of the
positioning errors sources and eliminate others; inonsphere
and troposphere effects are out of positioning equation.
Signal travel time has been shortened from 0.07 second to
about 0.000004 second. The aircraft altitude determination
has become more reliable since it refers to the real height of
the runway, not the mean sea level nor the earth ellipsoid like
GPS. Beside that, signal transmitted from Ground-based
system is stronger. It can penetrate construction in vicinity of
airport. Satellites unavailability due to satellites distribution
or construction blockage is a serious problem especially
within the approach and landing area. The problem has been
dealt with by accurate and calculated transmitters distribution
around the runway with different towers height to give a
wide visibility angle and provide accurate altitude
calculation. Therefore, vertical accuracy became as accurate
as horizontal accuracy. The receiver clock drift error can be
corrected by receiving signal from many transmitters since a
separated clock for each transmitter is used. Overall, this
system is completely autonomous. It does not depend on GPS
ISSN: 2231-5381
satellites such as DGPS where GPS errors are inherited and
involved in calculation, nor any other system.
In this system, the only sources of positioning error are signal
multipath and receiver noise. However, studies showed that
Multipath could be mitigated to centimeter level using new
techniques and antennas. In addition, modern and advanced
techniques use integrated hardware and improved algorithms
can reduce receiver noise to low levels. Studies indicated it
could be neglected even for high accuracy positioning since
its effect is in millimeter.
The calculated system specifications have been simulated to
evaluate the performance and test the capability of the system
to achieve aircraft accurate positioning. Trilateration
positioning equations have been solved using Matlab. A code
was established to indicate the aircraft position coordinates.
Aircraft approaching and landing have been simulated with
different positioning error sources. However, the real system
specifications results a position error of 0.2 m as multipath is
in the highest level. Simulations have been done showed that,
the accuracy of the system is in centimeter level.
The aircraft positioning simulations have been performed
comparing the system accuracy with current aircraft landing
systems. Results achieved showed that, this system is far
outperforming other systems. This system is 50 times more
accurate than GPS and 15 times more accurate than DGPS.
Some of GPS and DGPS accuracy reduction factors have
been eliminated and others have been reduced resulting a
high accurate all-weather system capable to achieve ICAO
recommended standards for CAT III C to enhance aircrafts to
land blindly.
For an easy access and simple indication of aircraft
approaching the runway, ILS style indicator has been
attached to indicate the aircraft position with respect to
runway and runway touch point. The indicator has been
http://www.internationaljournalssrg.org
Page 428
International Journal of Engineering Trends and Technology- Volume4Issue3- 2013
simulated using VisualBasic.net. It provides an accurate
aircraft deviation from recommended route points
coordinates enhancing the aircraft to land in all weather
conditions. Furthermore, this system can be used to guide
aircrafts to the parking lots in the airport. Finally, the
positioning results of simulation showed the performance of
the system. Compared with GPS, the majority of error
sources have been eliminated. Calculations and simulation
have been done showed that visibility, integrity, availability
and accuracy have been considerably increased.
Acknowledgement:
We would like to express our gratitude to Universiti Putra
Malaysia (UPM) for granting the Research University Grant
Scheme (RUGS) with Project No. 05-05-11-1560RU, in
which this research work is made possible.
[14]
[15]
[16]
[17]
[18]
[19]
[20]
[21]
6.
[1]
[2]
[3]
[4]
[5]
[6]
[7]
[8]
[9]
[10]
[11]
[12]
[13]
References:
A. T. Lisrary and K. Afb, “Controls , Displays , and Information
Transfer Controls , and Information Transfer for,” 1983.
“LANDING,” pp. 3–11, 2003.
M. Kayton, Navigation: Land, Sea, Air & Space. IEEE press,
1990.
L. Chittaro and S. Burigat, “3D location-pointing as a navigation
aid in Virtual Environments,” in Proceedings of the working
conference on Advanced visual interfaces, 2004, pp. 267–274.
U. Kingdom, “ROBUST NAVIGATION ALGORITHMS FOR
AIRCRAFT PRECISION APPROACH , LANDING AND
SURFACE MOVEMENT USING GLOBAL,” no. September,
2008.
P. Enge, “Local area augmentation of GPS for the precision
approach of aircraft,” Proceedings of the IEEE, vol. 87, no. 1, pp.
111–132, 1999.
J. Meyer-Hilberg and T. Jacob, “High accuracy navigation and
landing system using GPS/IMU system integration,” Proceedings
of 1994 IEEE Position, Location and Navigation Symposium PLANS’94, pp. 298–305, 1994.
S. Snyder, B. Schipper, L. Vallot, N. Parker, and C. Spitzer,
“Differential GPS/inertial navigation approach/landing flight test
results,” Aerospace and Electronic Systems Magazine, IEEE, vol.
7, no. 5, pp. 3–11, 1992.
J. Duke and V. Torres, “Multifactor productivity change in the air
transportation industry,” no. March, pp. 32–45, 2005.
R. Brown, G. Romrell, G. Johnson, D. Kaufmann, and X. Qin,
“DGPS category IIIb automatic landing system flight test results,”
in Position Location and Navigation Symposium, 1996., IEEE
1996, 1996, pp. 664–671.
S. Huang and M. Lee, “THE STUDY OF REAL-TIMED GPS
NAVIGATION ACCURACY DURING,” 2000.
J. David, W. Parkinson, J. Aubrey, U. Airlines, S. Francisco, A.
Group, N. Kaufmann, B. Commercial, B. David, M. View, A.
City, and J. Swider, “Autolanding a 737 Using GPS Integrity
Beacons,” vol. 42, no. 3, pp. 467–486, 1995.
B. Pervan, D. Lawrence, K. Gromov, G. Opshaug, J. Christie, P.
Y. Ko, A. Mitelman, S. Pullen, P. K. Enge, and B. W. Parkinson,
“Flight test evaluation of a prototype local area augmentation
ISSN: 2231-5381
[22]
[23]
[24]
[25]
[26]
[27]
[28]
[29]
[30]
[31]
[32]
[33]
[34]
system architecture,” in PROCEEDINGS OF ION GPS, 1997, vol.
10, pp. 1613–1622.
“Next Generation GPS Operational Control Segment (OCX)
Contract Awarded,” p. 20230, 2010.
“Satellite-based landing system certified (10.” .
A. Dissertation, “SIGNAL QUALITY MONITORING FOR GPS
AUGMENTATION SYSTEMS c Copyright by Alexander
Michael Mitelman 2005 All Rights Reserved,” no. December,
2004.
D. Lawrence, J. Evans, Y. Chalo, Y. Tsai, C. Cohen, T. Walter, P.
Enge, I. D. Powell, and B. Parkinson, “Integration of Wide Areia
DGPS with Local Area Kinematic DGPS,” 1996.
E. Meeting, R. Visual, and R. Speci, “AERODROME
METEOROLOGICAL OBSERVATION AND FORECAST
STUDY GROUP ( AMOFSG ),” no. 35, pp. 6–8, 2010.
“Terminal Area Separation Standards : Historical Development ,
Current Standards ,” 1997.
K. Bullington, “Radio propagation for vehicular communications,”
IEEE Transactions on Vehicular Technology, vol. 26, no. 4, pp.
295–308, Nov. 1977.
“Integration of Commercial Space Vehicle Traffic into the
National Airspace System,” 2012.
A. Mobile, C. Panel, W. Group, A. D. Prepared, B. Chateau, and
A. Item, “A GENERAL MODEL FOR VHF AERONAUTICAL
MULTIPATH PROPAGATION CHANNEL,” no. January, pp. 1–
24, 1999.
V. F. Maschinenbau and D. C. Vernaleken, Autonomous and AirGround Cooperative Onboard Systems for Surface Movement
Incident Prevention. 2011.
P. Boskoski, B. Mileva, and S. Deskoski, “Auto landing using
fuzzy logic,” pp. 2–8, 2005.
T. Gregorius and G. Blewitt, “The Effect of Weather Fronts on
GPS Measurements Ad Goes Here Keyline does not print Ad Goes
Here Keyline does not print.”
F. S. Solheim, J. Vivekanandan, R. H. Ware, and C. Rocken,
“Propagation delays induced in GPS signals by dry air, water
vapor, hydrometeors, and other particulates,” Journal of
Geophysical Research, vol. 104, no. D8, p. 9663, Apr. 1999.
R. Itu-r, “RECOMMENDATION ITU-R P.838-3 Specific
attenuation model for rain for use in prediction methods,” pp. 1–8,
2005.
C. Loo and N. Secord, “Computer models for fading channels with
applications to digital transmission,” IEEE Transactions on
Vehicular Technology, vol. 40, no. 4, pp. 700–707, 1991.
Y. Tsai, “The feasibility of combating multipath interference by
chirp spread spectrum techniques over Rayleigh and Rician fading
channels,” Proceedings of IEEE 3rd International Symposium on
Spread Spectrum Techniques and Applications (ISSSTA’94), pp.
282–286, 1994.
B. M. Hannah, “Modelling and Simulation of GPS Multipath
Propagation GPS Multipath Propagation.”
P. Hoeher, E. Haas, and D.- Kiel, “Aeronautical Channel Modeling
a t VHF-Band,” pp. 1961–1966, 1999.
G. A. Hajj and L. E. Young, “Assessment of GPS Signal Multipath
Interference,” 2002.
C. Rost and L. Wanninger, “Modelling and Correction of Carrier
Phase Multipath Effects,” no. July, 2012.
a. R. Amiri-Simkooei and C. C. J. M. Tiberius, “Assessing
receiver noise using GPS short baseline time series,” GPS
Solutions, vol. 11, no. 1, pp. 21–35, Apr. 2006.
http://www.internationaljournalssrg.org
Page 429