CAREER division consists of two kinds of users

CAREER
EPISODE 2

CHRONOLOGY

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Project Title: Real
Time Positioning, Construction and Implementation of a GPS-Communicator

Project Level: Master’s Thesis

Time Period: XXXXXXXXX
(XXXX 20XX to XXXX 20XX)

Duration: XXXXXXXXXXXXX

Location: Linköping University

Supervisor: Mikael
Göthammer

 

CE2.1       INTRODUCTION

In the project for my Master’s thesis, I performed an investigation that
outlines the different positioning systems, including GPS, DGPS, AGPS and GSM
positioning, as well as wireless communication techniques available in the
market, such as mobile internet connections through mobile phones and
communication via radio modems. Wireless communication techniques include HSCSD
(High-Speed Circuit-Switched Data), GPRS (General Packet Radio Service), UMTS (Universal
Mobile Telecommunications System) and MOBITEX. I performed this survey in aid
of KORDAB International AB, a Swedish company that wishes to expand its own
technical information system known as GEOSECMA by implementing a real time positioning
feature. This study assisted them in the selection of a system that will apply
this feature.

 

CE2.2       BACKGROUND

This project was motivated by the idea of answering several
questions by KORDAB in relation to their software system GEOSECMA, which is an IT-based
all-inclusive business solution that facilitates the decision making process as
well as linking of information and databases, for various business areas. KORDAB’s
proposal of contriving a positioning system to supplement  GEOSECMA considers two main points. They include:

·        
Which positioning system to use,
and

·        
Which communication linking
technique to use to provide the system with relevant position data, or how  the system’s interface will receive the
position data

 

The application of real-time positioning related to GEOSECMA is also
an interesting aspect, since during the implementation of the positioning
system, its potential uses will have to be taken into account so that the most efficient
system can be developed and integrated into the existing GEOSECMA.

 

CE2.3       SCOPE

A positioning system integrated with GEOSECMA not only enhances its
capabilities, but also adds another dimension to the utility of the system with
its own numerous facilities. Depending on the functionality needed from the
system, the applications are categorized based on the kind of users that will
use it. This division consists of two kinds of users – restricted, such as municipality
workers, and public, which includes the general population.

 

Restricted users’ applications are:

·        
Managing and controlling a
fleet of workers

·        
Logging locations

·        
Zooming and Auto-highlighting

·        
Alarms

For public users, the applications consists of:

·        
Find the best path to a chosen
point from the current location

·        
Find the best route to visit a
number of different locations (Travelling Salesman Problem)

·        
Finding information related to
one’s surroundings

 

CE2.4       LIMITATION

KORDAB’s insistence on developing a globally accepted, established interface
for a positioning system lead to some problems. Maintaining such a standard
could involve complex techniques as well as hefty expenses in order to modify,
update or change any component of the system. They also assert that the system
not be dependent on any particular product, resulting in separate interfaces
for each product which means that a lot of effort would be required to support
all such possible interfaces.

 

CE2.5       STANDARD
BODY REFERRED

The NMEA 0183 standard was referred to while conducting this examination.
NMEA 0183 is a combined electrical and data specification that facilitates communication
between a variety of instruments, including GPS receivers that we have used in
this project.

 

CE2.6       OBJECTIVE

The biggest issue associated with the current GEOSECMA system is the
lack of a positioning system that can receive relevant position data from the
GEOSCEMA system interface and act on it to fulfill various needs of the users. This
positioning enhancement to GEOSCEMA needs to be implemented by choosing the
best wireless connection techniques along with a positioning system from a
range of available choices. Each method has its pros and cons and a thoroughly
detailed investigation was conducted by me to evaluate them one by one. The positioning
system to be developed must be able to cater to different kinds of users as
well as have a standardized interface so as to ensure internationally
acceptable standard and quality.

 

CE2.7       TEAM
STRUCTURE

I made this project with one other student, who is also a student of
Masters in Science in the field of Control and Communication. Thus our two
member team performed the various activities and tasks associated with the
project.

 

Our
supervisor at KORDAB, Mikael Göthammer, regularly gave us the perspective of
the KORDAB team which was extremely essential as the investigation was done on
their behalf and it was essential to understand their requirements from the
system. He also monitored our survey to ensure we were going along the right
path. Our tutor, Ulf Henriksson, who is also the Head of the Department, regularly
reviewed our work and finalized our submission to the Education and Research
Council.

 

 

 

 

 

 

FIGURE 1: TEAM STRUCTURE

 

CE2.8       THEORETICAL
ASPECTS

The theoretical portion of this project was concerned with the evaluation
of various potential positioning methods and communication techniques that can be
used to implement a positioning system with GEOSECMA.

 

Positioning Methods

 

·        
GPS: The Global Positioning
System requires only a GPS receiver in terms of equipment and the accuracy of
the system is affected by the kind of receiver used, along with several other
factors. Generally, survey grade GPS receivers provide better accuracy (about
1m) while consumer grade GPS receivers provide an accuracy between 5m to 25m.  Accuracy is also affected by details such as
antenna configuration, bias errors and satellite constellation status. The cost
of the receivers depends on the brand and quality chosen, however, a cheaper
cost does not usually indicate poor quality.

·        
DGPS: A Differential Global
Positioning System consists of two GPS receivers, one that is mobile, taking
the actual measurements while the other is stationary, which receives signals
from the GPS satellites. The expenses associated depend on the type of GPS receivers
as well as service providers selected.

·        
RTK GPS: A Real Time Kinematics
GPS makes use of measurements from the signal’s carrier wave, instead of
information contained in the signal and provides real-time corrections, leading
to a very high accuracy (up to 1 cm).

·        
AGPS: Assisted GPS utilizes cell
tower data along with the information obtained from GPS satellites to improve quality
and precision in cases when satellite signal conditions are not strong enough
by themselves. Network providers usually cost extra for access to the external
data. AGPS provides accuracy of up to 50m indoors and about 15 m for outdoors.

 

Communication Links

 

·        
Mobile Internet Connection:

§  GSM: Global System for Mobile Communications is a digital,
circuit-switched network that allows voice telephone calls. GSM requires a
connection to be established and the users to stay connected throughout the
duration of the data transfer process. In addition, a GSM phone or modem is
also required.

§  HSCSD: High-Speed Circuit-Switched Data is a faster implementation of
GSM, however it has less error protection capabilities.

§  GPRS: General Packet Radio Service is packet-switched, instead of
using circuit-switching techniques like GSM. This implies that the costs of
GPRS depend on the amount of data used, instead of the connection duration.

§  UMTS: Universal Mobile Telecommunications System provides a variety
of services along with voice phone calls such as messaging and Internet by making
use of wideband Code Division Multiple Access (W-CDMA) technology.

 

·        
Mobitex(Radio Modem): Mobitex
was developed by Ericsson and Televerket and is a wireless packet-switched
network in which, data transfers are not affected by voice calls. One needs a
subscription with a Mobitex network 
provider as well as a modem to make use of a Mobitex network.

 

·        
Internal Radio Modem Network: These
networks can be configured in a variety of topologies and involve the use of one
or more base stations. The costs associated with the network depend on the
chosen configuration as well as several other factors.

 

CE2.9       CALCULATIONS

GPS Pseudorange

The calculation of pseudorange, R is done as:

 

 

where,

c denotes the speed of light,  stands for the time difference,  refers to the distance between the satellite
to the receiver,  denotes distance from geocenter to satellite
and  denotes the distance from the geocenter to receiver.

 

Pseudorange Correction using DGPS

Corrected pseudorange =
c. (tmeasured – tcorrectionfactor)

where c is the speed of
light, tmeasured stands for the measured time for the signal to
arrive and  tcorrectionfactor denotes
the time correction factor.

 

 

 

 

 

 

 

 

 

 

 

 

FIGURE 2 : GPS
PSEUDORANGE CALCULATION

 

CE2.10   TEAM
CONTRIBUTION

The project was divided into the following stages:

 

1. Requirements Gathering

2. Thorough Examination

3. Analysis of Results

4. Conclusion, i.e., Selection of the Best Methods

 

In order to make sure that the survey was done in an effective
manner, we divided the tasks amongst ourselves to get the best use out of the
available resources, the given time and our own abilities.

 

CE2.11   PERSONAL
ENGINEERING ACTIVITY

As we had a deadline to meet and limited resources available, we
divided the tasks required to complete the project amongst the project team
members. I was responsible for the theoretical investigation of the various positioning
systems and communication techniques, as described in the Theoretical Aspect
section, CE2.9.

 

I also investigated the NMEA 0183 protocol, that is used by positioning
units like GPS and DGPS receivers of positioning systems. This standard from the
National Marine Electronics Association uses an ASCII based serial
communications method which allows data to be multicasted, i.e., sent from one
sender to multiple receivers. It basically includes the definition of
electrical signal requirements, data transmission protocol, timing and specific
sentence formats.

 

NMEA Electrical Interface

NMEA employs an asynchronous interface with the parameters:

Baud rate: 4800
Number of data bits: 8 (bit 7 is 0)

Stop bits: 1 (or more)

Parity: none

Handshake:  none

 

NMEA Sentence Format

The first word of NMEA sentences is called a data type which
explains the rest of the sentence. The GPS receivers only decipher those sentences
that start with data types they’re interested in, all other sentences are
ignored. These sentences can be 82 characters long and some of their examples are:

AAM –
Waypoint Arrival Alarm

ALM –
Almanac data

 

NMEA Hardware Connection

NMEA specifies the requirements for the hardware interface of GPS
units. It recommends conformance with the EIA-422 standard as well as an
interface speed of 4800 baud/s. This means that 480 characters can be sent in
one second. A cable is needed to use the hardware interface.

 

CE2.12   SIMULATION

A GPS needed to be simulated in order to find out the best
positioning methods, however, instead of using a real GPS, we decided to use a
terminal program since when GPS is used indoors, it requires an external antenna
outside to receive signals from the satellites. The terminal program that we
used is able to completely imitate a real GPS receiver. To work properly, it
required a text file that consists of logs of data being sent from a GPS that
is connected to the terminal program, as well as a portable computer that could
be taken outside to receive GPS signals. The terminal program we utilized is
called RecSimIII.

 

CE2.13   RESULT

The results of the preliminary study helped us identify which positioning
systems, communication techniques and design interface would be most useful to
KORDAB when employed in a real-time positioning system. The survey led us to
the conclusion that GPS along with DGPS employed for correction would be the
best positioning system to apply, since these systems follow a standardized
protocol (NMEA 0183) that no other system does. The best communication link KORDAB
can use would be one that uses a pre-existing ISP connection, since GEOSECMA
already has a web layer that uses Internet. So, a GPRS or GSM connection link
would be the most ideal. The design interface must follow NMEA 0183
specifications since GPS and DGPS receivers would be used.

 

CE2.14   DOCUMENTATION

The related information was logged at every step of the
investigation and simulation during the project by both team members. The final
stages  in the project involved a
thorough analysis of the collected data and coming to conclusions on the most
suitable methods for our purpose. Once this stage is completed, the gathered
information is compiled and formatted into a final report format and submitted
to the Head of the Department.

 

CE2.15   SUMMARY

Involving
myself in this project gave me the opportunity to explore my investigative as
well as analysis abilities. I learned how to pay extreme attention to detail so
as to not miss any important points and I also understood how to evaluate all
the available alternatives with respect to the given requirements for the final
system. Overall, working on this project helped me enhance many of my technical
abilities that will definitely be of help in the coming years.

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