Improvement of GPS performance using SNR information analysis
Jong-woo An1, Yun-Ki Kim2, Jin-Ho Kim3 ,Yo-Seop Hwang4 and Jang-Myung Lee6
1,2,3,4
Pusan National University, Korea, Republic of
(Tel: 81-51-510-7379, Fax: 81-51-514-1696)
5
Pusan National University, Korea, Republic of
(Tel: 81-51-510-2378, Fax: 81-51-514-1696)
1
jongwoo7379@pusan.ac.kr, 2mecha8404@pusan.ac.kr, 3jinho7379@pusan.ac.kr,
4
mmx001@pusan.ac.kr, 5jmlee@pusan.ac.kr
Abstract: In general, GPS signal, structure, these errors geometric error occurs, the degree is severe enough low-cost
GPS.Of course using a GPS or RTK system, it is possible to know the position accuracy location estimates.But, such as
these systems have the disadvantage that high cost and need to reference stations station for adjust the
position.Recently, intelligent robot industry which is mobile function equipped to provide more convenient services to
users is expanding.In order to provide move convenient and accurate service to users, the process. In the activation of
intelligent robot industry, many costly for the exact position estimation of the robot, it becomes an obstacle. In this
paper, traceback the GPS receiver location by using the pseudo distance between the satellite ephemeris and satellite
receiver. We will progress the pre study to obtain precise position by using the SNR value obtained by the estimated
value.
Keywords: Mobile Robot, GPS, Satellite, Localization
1 INTRODUCTION
This paper is pre study to obtain more precise location
information using by satellite orbit information, pseudo
range and SNR information instead of NMEA 0183
Protocol provided by the GPS. Recently, intelligent robot
industry which is mobile function equipped to provide more
convenient services to users is expanding. In order to
provide move convenient and accurate service to users, the
process. This is because when intelligent robot do not know
own location, there are difficulties to performing the given
task. Although exactly recognizing the own position of the
intelligent robot is basic intelligence to provide services to
users, It is bottlenecks technology that is hard to overcome
by the factors such as peripheral environment, technology
and development cost. Many manpower like Universities,
industry and research institutes are investing time to
develop location recognizing technology. Although location
recognizing technology has technically providing guidance,
It is questionable whether it has the investment value
because it has lots of shortcomings like price, reliable
technology and technical perfection. But the industry
related to the quality of human life has emerged as a future
technology. Based on these trends, in order to enrich the
quality of human life, intelligent robots are expected to play
an important role. And also in order to intelligent robot
industry becomes active, location recognizing technology
that has high accuracy is needed. Of course, It is able to
obtain the precise location information by using the
DGPS(Differential Global Positioning System) and
RTK(Real Time Kinematic) system. DGPS and RTK
systems require a number of fixed reference stations to
provide more precise location information and receiver that
is capable of receiving the carrier wave to obtain a position
compensation information to be transmitted from the
reference station.
Also There is disadvantage. It cost high making the network
to installing reference stations and conjugate it.
In this paper, we proceed with the pre-study to overcome
these disadvantages and improve the performance of lowcost GPS receiver using the SNR information. SNR means
the signal to noise ratio, and it shows the degree to which
the signal is distorted by the noise generated in the course
of transmitting a signal from the satellite. Generally, when
SNR value is higher, distortion of the signal is low.
Generally, the SNR value is higher to the distortion of the
signal that the enemy, The reason for this can be seen by the
equation defined as follows.
SNR 
signal strength
noise
(1)
Like a formula shown in the above, when divide the noise
from the original signal strength it become the SNR value.
And the smaller the amount of noise at the same signal
strength, SNR value become large. In this paper, traceback
the GPS receiver location by using the pseudo distance
between the satellite ephemeris and satellite receiver. We
will progress the pre study to obtain precise position by
using the SNR value obtained by the estimated value.
2 Location recognizing
Estimation of using GPS is single determination and
absolute determination. In this paper, using single
determination Pseudo-range of GPS and Receiver. And
receive from GPS orbit of satellite using GPS location
receiver of estimation.
2.1 Calculation of Pseudo-range
Single determination is method for determining the
position in the Code Tracking, method, In one receiver,
suah as Figure 1 after observing the four or more satellites,
using the pseudo-range and calculates the position. In this
context, the pseudo-range is in the process of receiving a
GPS signal, including a distance error between the number
of factors that can be generated by the satellite and the
receiver refers to the distance of the computed satellite and
the receiver.
UBX protocol may collect information about the broadcast
ephemeris also between Using the satellite and the receiver
described in 2.1 UBXprotocol doctors are also readily
available on the street. In figure 2 is follows structure of
UBX protocol.
Figure 2 UBX Protocol
UBX protocol provides the same information as is shown in
Table 2 for each class ID.
Figure 1. 단독 측위법
Between satellite and Pseudo-range is define as follows:
r i A  ( X i  X A )2  (Yi  YA )2  (Zi  Z A )2  c
(1)
ri
A is Pseudo-range to the receiver means he A
where (1),
from the satellite I, and the unit is meter. C refers to
3.0 108 m/s the speed of light in vacuum.  is the
clock deviation between satellite and the receiver. Ahead of
the intersection of several factors are included, but the error
occurs, formula (1) is a basic formula to establish the
assumption that there are many types of errors. if receiving
the data from four or more satellites in the GPS receiver,
the formula (1) composed of at least four between applying
the least square method in the position of
X A , YA , Z A
and
clock deviation(  ) of a receiver of GPS and each
satellite doctor can get a distance.
Table 1 UBX protocol Class
NAME Class ID
Description
NAV
0x01
Navigation Result
RXM
0x02
Receiver Manager Messages
INF
0x04
Information Messages
ACK
0x05
Ack/Nack Messages
CFG
0x06
Configuration input Messages
MON
0x0A
Monitoring Messages
ADI
0x0B
AssistNow Aiding Messages
TIM
0x0D
Timing Messages
ESF
0x10
Ex
In this paper, UBX protocol can obtain the value of the
RXM-EPH and RXM-RAW, it parameters necessary for the
RXM-SFRB calculate the position of the satellite to provide
the type of service in the RXM. Required to calculate the
position of the satellite fomula as follows.
SatX  Xdash *cos(Wc)  Ydash *cos( I )*sin(Wc)
(2)
SatY  Xdash *sin(Wc)  Ydash *cos( I )*sin(Wc)
(3)
2.2 Location Recognizing of Satellite
The Control of GPS is composed of a MCS(Master Control
Station and unattended five Monitor Station Operatiing.
Generally, Broadcast Ephemerides determines a reference
orbit for each satellite to calculate the trajectory of the
satellite based on the data accumulated for one week at 5
Monitor Station. In general, the NMEA 0183 protocol used
by the GPS does not provide information on the Broadcast
Ephemerides, the UBX protocol provided by the in-house
developed in U-Blox use to obtain information for the
broadcast ephemeris. Of course, if only to be used a Ublox's GPS receiver to use Timing model among them the
SatZ  Ydash *sin( I )
(4)
Using the Formula (2), (3), (4) to obtain basic information
about the coordinates of the satellite. And to obtain the final
satellite coordinates using the following formula. The
position of the satellite is calculated considering the Earth's
rotation.
SVx  SatX *cos(alpha)  SatY *sin(alpha)
(5)
SVy  SatY *cos(alpha)  SatX *sin(alpha)
(6)
SVz  SatZ
(7)
Alpha  tau *Wedot
(8)
The formula (8) of the amount of Earth's rotation, ask the
coordinates of the satellite through the above expression
can be determined the position of the receiver using the
following equation.
Figure 3. EVK-M8T
SVxi  Rx
Ri
SVyi  Ry
Dyi 
Ri
SVzi  Rz
Dzi 
Ri
Dti  1
Dxi 
(9)
(10)
Figure3 is the use u-Blox, Inc. EVK-M8T to experiment to
try to progress in this paper. As noted in Chapter 2, to
obtain the data to be studied in this paper, we are advancing
the experiments using the u-Blox Company T series models.
(11)
(12)
With the Dxi , Dyi , Dzi , Dti and (13), (14), (15),
(16), (17), it is possible to track the position of the GPS
receiver.
 Dx0
 Dx
A 1
 Dx2

 Dx3
Dy0
Dy1
Dy2
Dy3
Dz0
Dz1
Dz2
Dz3
dR  ( AT * A)1 * AT * L
Rx  Rx  dR0
Ry  Ry  dR1
Rz  Rz  dR2
Dt0 
Dt1 
Dt2 

Dt3 
(13)
(14)
Figure 4 Reference
It is promoting an experiment in South Korea in Pusan
National Univ playground, to collect the data by attaching a
GPS to the people, by simulation using the collected data to
proceed in the direction you want to see the results. Figure
4 shows the reference
(15)
(16)
(17)
Write a Matlab code based on the above formula and
Section 3, using the u-Blox's EVK-M8T and to proceed
with the experiment to estimate your location.
3 Experiment
Figure 5 Simulation
Figure 5 is a result of the estimated position of the GPS
receiver using a Matlab. It means the X axis is of the X-axis
of the ECEF and Y axis is Y-axis of the ECEF
(2004), The Journal of the Korean Society of Surveying,
Geodesy, Photogrammetry and Cartography 22(4), Korea,
Dec 31, 2004, pp.383-390
Figure 6 Google Earth
Figure6, based on the results of the simulation were
confirmed via Google Earth to the position of the user
estimated by using the NMEA0183 protocol and UBX
Protocol. Green, existing NMEA data, blue is the UBX data.
4 CONCLUSION
This paper is pre-study to improve the performance of the
GPS receiver using the SNR information. To estimate the
position of the GPS receiver that uses a pseudo range of
experimental results satellite coordinates and the doctor is
necessary still a lot of research. Future advances the
research of the position recognition using a mobile robot,
and after visible results similar to existing GPS data, by
using the SNR information, and is a plan to advance
research for improving the position estimation precision.
ACKNOWLEDGEMENT
This research was supported by the MOTIE (Ministry of
Trade, Industry & Energy), Korea, under the Industry
Convergence Liaison Robotics Creative Graduates
Education Program supervised by the KIAT (N0001126)
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