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authorRefik Hadzialic2012-09-02 11:39:54 +0200
committerRefik Hadzialic2012-09-02 11:39:54 +0200
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parentImplementation OpenBSC description (diff)
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Modification of intro chapter!
-rw-r--r--vorlagen/thesis/maindoc.pdfbin17547801 -> 17550874 bytes
-rw-r--r--vorlagen/thesis/src/erklaerung.tex22
-rw-r--r--vorlagen/thesis/src/kapitel_x.tex353
3 files changed, 209 insertions, 166 deletions
diff --git a/vorlagen/thesis/maindoc.pdf b/vorlagen/thesis/maindoc.pdf
index a9ea9bb..013943b 100644
--- a/vorlagen/thesis/maindoc.pdf
+++ b/vorlagen/thesis/maindoc.pdf
Binary files differ
diff --git a/vorlagen/thesis/src/erklaerung.tex b/vorlagen/thesis/src/erklaerung.tex
index 860857c..09b2d3e 100644
--- a/vorlagen/thesis/src/erklaerung.tex
+++ b/vorlagen/thesis/src/erklaerung.tex
@@ -22,23 +22,23 @@ Unterschrift \\(Signature)
Acknowledgment}
I would like to thank my supervisors Konrad Meier and Dennis Wehrle for their
-help and encouraging talks during the thesis. Beside the help from the supervisors I
-would like to thank my family and friends who supported me through my master studies, and
-the entire Communication systems department for their support, free coffee and
+help and encouragement during the thesis. Besides the help from my supervisors I
+would like to thank my family and friends who supported me through my master's degree, and
+the entire Communication Systems department for their support, free coffee and
to Prof. Dr. Gerhard Schneider for making all the required hardware available. I would like
-to thank Prof. Dr. Christian Schindelhauer for writing the recommendation letter so that DAAD
+to thank Prof. Dr. Christian Schindelhauer for writing the recommendation letter so that the DAAD
could extend my scholarship and stay in Freiburg.
-I would like to thank my friend Mirza Hamza from the Telecommunication department at the Faculty
+I would like to thank my friend Mirza Hamza from the Telecommunications department on the faculty
of Electrical Engineering in Sarajevo for proofreading the AGPS chapter.
I would like to thank Sebastian Schmelzer for
-his LaTeX tips, Michael Neves Pereira and Jonathan Bauer for borrowing me their cell
-phones to test my localization system with as well as Johan Latocha for patiently explaining
-me words I did not understand in the German language and for showing me Inkscape.
+his LaTeX tips, Michael Neves Pereira and Jonathan Bauer for lending me their cell
+phones to test my localization system as well as Johan Latocha for patiently explaining
+words I did not understand in the German language and for showing me Inkscape.
I would like to thank Richard Zahoransky
-for the helping discussions about various GSM topics. Thank go to Holger Hans Peter Freyther
-as well, who gave me a hint where to modify OpenBSC to make an independent data channel interface
+for the helpful discussions about various GSM topics. Thanks to Holger Hans Peter Freyther
+as well, who gave me tips on how to modify OpenBSC to make an independent data channel interface
with a cell phone. Things which have not been done before
-are intellectually seductive in some way and it kept me motivated and working during the tough
+are always intellectually seductive and this kept me motivated and working during the tough
periods.
\newpage
diff --git a/vorlagen/thesis/src/kapitel_x.tex b/vorlagen/thesis/src/kapitel_x.tex
index 0ab4210..91b5cb0 100644
--- a/vorlagen/thesis/src/kapitel_x.tex
+++ b/vorlagen/thesis/src/kapitel_x.tex
@@ -1,80 +1,81 @@
\chapter{Introduction}
\section{Motivation}
Recent developments in the field of physics, chemistry and electronics
-have led to cheap and compact size
-manufacturing of diverse single chip integrated solutions. As a consequence of the
+have led to the cost-efficient
+manufacturing of diverse, compact single chip integrated solutions. As a consequence of this
rapid development it became possible to integrate a GPS receiver into almost every cell
phone without drastically increasing the price, physical size or weight of
the cell phone. An example of this would be the GPS receiver chip
-inside the Apple iPhone 3GS, the cost was estimated to be around \$2.25 USD \citep{GPSiphoneCost}.
-It is important to note, the number of wireless connections has increased as well,
+inside the Apple iPhone 3GS. Its cost was estimated to be around \$2.25 USD \citep{GPSiphoneCost}.
+It is important to note that the number of wireless connections has increased as well;
in 2011 there were
6 billion mobile connections worldwide \citep{gsmConnection}. In the following European
countries, Germany, France, Spain, Italy and UK, 44\% of all GSM users own a smart phone,
whereas in the US and Canada this number is slightly higher, 46\% \citep{smartPhoneUsage}. By the
-statistics of the Blur group 47\% of all the cell phones on the world shall be smart phones
+statistics of the Blur group, 47\% of all the cell phones on the world will be smart phones
by 2015 \citep{smartPhone2015}.
-An emerging new market of location based services (LBS) have grown out of it and since then
-changes the telecommunication and marketing industry with fast pace. In 2009, 63 million users
-used some of the LBS on their cell phones, this number is expected to grow in 2012 to
-468 million users worldwide \citep{smartPhone2015}. As social networks grow like Facebook,
-Twitter or Foursquare (a location based social network), it has become a trend
+An emerging new market of Location-Based Services (LBS) has resulted and since then
+the telecommunication and marketing industry have undergone rapid change. In 2009, 63 million users
+owned LBS-capable phones. This number is expected to grow in 2012 to
+468 million users worldwide \citep{smartPhone2015}. As social networks like Facebook,
+Twitter or Foursquare (a location-based social network) expand, it has become a trend
for the users to share their location with their friends \citep{smartPhone2015}.
-It has been reported that LBS represent a bonanza opportunity for new startup
-companies and Global Industry Analysts project by 2015 a global market
-worth of \$21 USD billion ($\approx$ \euro17.142 billion) \citep{Bonanza}.
+It has been reported that LBS represents a bonanza opportunity for new startup
+companies and global industry analysts project by 2015 a global market
+worth \$21 USD billion ($\approx$ \euro17.142 billion) \citep{Bonanza}.
New ideas and algorithms for tracking,
-navigation solutions, safety, security, local business search and payments shall emerge
-from it as well as the new market that shall emerge from the results of data mining
-user's movement \citep{Bonanza}. LBS have been used for tracking people with dementia, Alzheimer's
-disease, as reported in a study performed by the University of Siegen \citep{Muller}.
+navigation solutions, safety, security, searching for local business and payments shall emerge
+from the use of LBS technology \citep{Bonanza}. LBS have already been used for tracking people with dementia and Alzheimer's
+disease, as reported in a study performed by researchers at the University of Siegen \citep{Muller}.
The Enhanced 911 (E911), an emergency service in the US for linking
-emergency callers with appropriate public service (police, firefighters and emergency room),
-regulated with the US Federal Communication Commission (FCC) a standard for all telecommunication
-providers to have capabilities of localizing their users within a defined range \citep{novine}.
-Similar standards exist for Europe's E112 service as well \citep{0849333490}. Next generation
-networks, long term evolution (LTE) 4G networks, have been designed from the start to have LBS capabilities integrated
-in the system and even a better LBS performance as well as accuracy compared to GSM networks \citep{lteLocation}.
-In the introductory chapter, some of the most known positioning techniques in
-wireless networks shall be presented and analysed, Cell-ID, time of arrival, angle of
-arrival and GPS positioning. Then the author shall proceed and describe the goals of his thesis.
+emergency callers with the appropriate service (police, firefighters and emergency room), is
+regulated by the US Federal Communication Commission (FCC), which sets the standards for all telecommunication
+providers, including the precision with which callers' locations are tracked \citep{novine}.
+Europe's emergency service has similar standards \citep{0849333490}. Next generation
+networks, Long Term Evolution (LTE) 4G networks, have been designed from the start to have LBS capabilities integrated
+in the system and have better LBS performance as well as higher accuracy compared to GSM networks \citep{lteLocation}.
+In the introductory chapter, some of the most common positioning techniques in
+wireless networks shall be presented and analysed, including Cell-ID, Time-of-Arrival, Angle-of-Arrival
+and GPS positioning. The author shall then describe the goals of his thesis.
+In this thesis the author shall provide the theoretical and practical
+knowledge required for building a localization system of mobile users
+inside of a 2G GSM network by taking advantage of the already-existing AGPS receivers inside of smart phones.
\newpage
\section{Positioning techniques}
-In this section related technologies for estimating the position of a mobile user shall be presented
+In this section, the current technologies for estimating the position of a mobile user shall be presented
and their working principle.
When the GSM network was designed, its primary goal was to enable wireless
-full duplex telephony service \citep{gsmTelephony}.
-Over the past decade the GSM and its follower networks became more popular and mature compared to the initial GSM standard so
-the demands grew for different services. One of the demands, was the demand from emergency services
-to localize mobile user in emergency situations like snow avalanches or other not
-typical daily emergency situations \citep{0849333490}. This demand led to the
-devolopment of different approaches that differ in complexity and in the degree of accuracy of position fixes.
-However, the user positioning was limited by using existing technology standards
-without making extremely expensive cost modifications to the existing network infrastructures. With
-regards to costs and existing infrastructure, different ideas have been developed to localize mobile users.
-They shall be presented in the following sections but before the details are revealed it is important to
-distinguish three different approaches to positioning mobile user's, handset, network and hybrid-based
-approach. The handset based techniques are based on one fact, the handset itself tries to estimate its
-position using the available information on its own. In the network based approach the network makes
-all the required measurements and the handset itself is passive. The last approach, hybrid based, uses
-resources from the handset and network together, both are active participants in the position estimation process. In
-the further text with mobile station the target user one wants to locate is ment. A few different methods,
-varying by their complexity and precision, shall be presented. First simple and then more advanced techniques
-shall be presented in their complexity order.
+full duplex telephone service \citep{gsmTelephony}.
+Over the past decade the GSM and its derivative networks became more popular and mature compared to the initial GSM standard, so
+the demands grew for new services such as Internet connectivity and LBS. Emergency services wanted
+to be able to localize mobile users in emergency situations like snow avalanches or other non-typical
+daily emergency situations \citep{0849333490}. This demand led to the
+devolopment of various approaches that differ in complexity and in the degree of accuracy of position fixes.
+However, the user positioning was limited by existing technology standards, and any improvement would require extremely
+expensive cost modifications to the existing network infrastructures. Several different ideas have been put forward to
+localize mobile users while avoiding these potential problems.
+They shall be presented in the following sections. First, however, it is important to
+distinguish between three different approaches to positioning mobile users, handset-based, network-based, and hybrid-based.
+With handset-based techniques, the handset itself tries to estimate its position on its own using the available information.
+In the network-based approach, the network makes
+all the required measurements and the handset itself is passive. The last, hybrid-based, approach uses
+resources from the handset and network together; both are active participants in the position estimation process.
+For the purposes of this thesis, the term ``Mobile Station'' will be used to designate the user one intends to locate.
+A few different methods, varying by their complexity and precision, shall be presented, in order of their complexity.
\subsection{Cell-ID}
-Cell-identification method is the simplest known GSM ranging method \citep[Chapter 8]{0470092319}.
-By knowing the geographical location of the base transceiver
-station (BTS) one can roughly estimate the position of the mobile station (MS) \citep[Chapter 4]{0470694513}.
+The cell-identification method is the simplest known GSM positioning method \citep[Chapter 8]{0470092319}.
+By knowing the geographical location of the Base Transceiver
+Station (BTS), one can roughly estimate the position of the Mobile Station (MS) \citep[Chapter 4]{0470694513}.
It is important to build maps where the BTS signal can be received and where the border \textit{handover} points
are located. Handover is the process of switching from one BTS to another where the signal reception strength
-is higher than on the currently connected BTS.
+is higher than on the currently-connected BTS.
The basic principle is shown in figure \ref{img:cellid}. The BTS are
divided into geographical regions\footnote{Usually they are represented as hexagons but it could take
-any other geometric shape!} by their signal coverage. The MS is in the region of the currently connected BTS
+any other geometric shape.} by their signal coverage. The MS is in the region of the currently-connected BTS
and it could be at any point inside of the hexagon. Every
BTS has a unique identifier code name and hence can be distinguished from other BTS's.
@@ -86,42 +87,42 @@ BTS has a unique identifier code name and hence can be distinguished from other
\end{figure}
Using this method even higher accuracies
-can be achieved than the known shape of signal reception \citep[Chapter 8]{0470092319}. Basically, provided that the
+can be achieved than the known shape of signal reception \citep[Chapter 8]{0470092319}, provided that the
\textit{timing advance} (TA) value is known. The TA is the rough prediction of the \textit{round trip time} (RTT), time
required for a data packet to be received and acknowledged by the MS. Using this measure a rough circle can be made between
-the BTS and the bordering points of the Cell-ID region since TA multiplied with speed of light produces the radius distance
+the BTS and the bordering points of the Cell-ID region since TA multiplied by the speed of light produces the radius distance
of the circle. To obtain the TA value a connection between the MS and the BTS has to exist or a silent call can be made
where the GSM subscriber does not even notice that he/she is being called since there is no ringing
or any other sign that an idle connection is being performed on the MS \citep[Chapter 4]{3GPPTS03.71}.
-If there are more antennas than one, then it can be even further specified where the MS is positioned.
-This can be still inaccurate because of the multipath signal reflections.
+If there are more antennas than one, then the MS location can be even more precisely specified.
+This can still be inaccurate, however, because of multipath signal reflections.
In urban environments it is usually the case that there is no optical line of sight between the BTS and MS,
-so while the signal propagates from the BTS to the MS and vice versa it may get reflected from multiple buildings
+so while the signal propagates from the BTS to the MS and vice versa it may be reflected by buildings
or other objects which add extra propagation time (extra range to the distance). The accuracy of this method is typically
in a range of 200 m \citep{Zeimpekis}.
-This method can be seen both as a handset and network based position
+This method can be seen both as a handset- and network-based position
estimation technique, due to the fact that the user may run his/her own application on the cell phone or it can be applied by
-the network operator himself. This estimation technique does not require the MS to be a smart phone, it works with
+the network operator himself. This estimation technique does not require the MS to be a smart phone; it works with
any type of cell phone.
\subsection{Received Signal Strength}
The Received Signal Strength (RSS) position estimation technique, as the name states,
uses the signal strength measurement reports to localize the MS. RSS measurement
-reports in GSM networks are transmitted from the MS to the BTS and they
+reports in GSM networks are transmitted from the MS to the BTS and they
are used to determine if the handover process should be triggered or not \citep{Richard2011Master}.
\begin{figure}[ht!]
\centering
\includegraphics[scale=0.50]{img/RSS.pdf}
\caption{Basic idea of the RSS estimation technique. One rectangle location is represented by two
- RSS measurements for two BTS, blue is BTS1 and red is BTS2.}
+ RSS measurements for two BTS, blue indicates BTS1 and red indicates BTS2.}
\label{img:rssLoc}
\end{figure}
-This method requires mapping the location blocks with RSS of the
-covered areas before it can be used \citep{Richard2011Master}. The basic
+This method requires mapping the location blocks of the covered areas with RSS
+before it can be used \citep{Richard2011Master}. The basic
idea can be seen in figure \ref{img:rssLoc}, where one location region is represented
by two differently colored (blue and red) RSS measurements inside of one rectangle.
-By knowing pre advance the RSS one can estimate
+By knowing the RSS in advance one can estimate
the probability that the MS is located in the black rectangle.
Since it is difficult to measure the RSS at every point, the map is interpolated with
RSS using the Voronoin interpolation to calculate the expected RSS at places were
@@ -135,98 +136,98 @@ require a smart phone. It is a network based estimation technique.
\subsection{E-OTD and UL-TDOA}
\label{LMUSync}
-E-OTD and UL-TDOA are two similarly working positioning techniques, both use the time difference of
-signal arrival and for this reason have been grouped as one.
+E-OTD and UL-TDOA are two similar positioning techniques; both use the time difference of
+signal arrival and for this reason have been grouped together.
E-OTD stands for Enhanced Observed Time Difference. This technique requires the GSM network to be
-clock synchronized. The clock synchronization of the GSM network can be achieved with
-a location measurement unit (LMU) \citep{ETSI.TS.125.111}. LMU's provide the precise time to the BTS's
+clock-synchronized. The clock synchronization of the GSM network can be achieved with
+a Location Measurement Unit (LMU) \citep{ETSI.TS.125.111}. LMU's provide the precise time to the BTS's
by having an atomic clock synchronized with the BTS on a seperate location from the BTS or
-by providing a special GPS device at the BTS location that can provide precise time \citep{ETSI.TS.125.111}.
-The clock synchronization of the MS and the BTS is required becase the E-OTD technique
+by providing a special GPS device at the BTS' location that can provide the precise time \citep{ETSI.TS.125.111}.
+The clock synchronization of the MS and the BTS is required because the E-OTD technique
takes advantage of measuring signal propagation time.
-A data signal with current time information is transmitted from three or more spatially distinct BTS's at the same time
+A data signal with precise up-to-date time information is transmitted from three or more spatially distinct BTS's at the same time
and then propagation time is measured on the MS (all these BTS's must be detecable by the MS itself) \citep{200mRangeEOTD}.
-Once the difference in time is known between the time point when the signal was transmitted and when it was received,
+Once the difference in time is known between when the signal was transmitted and when it was received,
it is easy to estimate the relative position to the BTS's with hyperbolic trilateration \citep{200mRangeEOTD}
\citep[Chapter 4]{3GPPTS03.71}.
-In order to estimate the absolute position, it is required to know
+In order to estimate the absolute position, one must first know
the absolute location of the BTS's. The basic idea can be seen in figure \ref{img:eotdLoc}.
\begin{figure}[ht!]
\centering
\includegraphics[scale=1.20]{img/EOTD.pdf}
\caption{Basic idea of the E-OTD positioning technique. Current time information
- are transmitted from 3 different BTS's at the same time.Then the MS observes the difference of time when
+ is transmitted from 3 different BTS's at the same time. Then the MS observes the difference of time when
the information arrive and using trilateration technique calculates the relative position of
the MS.}
\label{img:eotdLoc}
\end{figure}
-E-OTD requires the cell phone to be equiped with the firmware software to perform the measurements but does
+E-OTD requires the cell phone to be equiped with firmware to perform these measurements but does
not require new or external hardware. The accuracy of this method lies in the range between 50-200 m, depending
-on the location of the MS \citep{malik2009rtls}. This method is not resistant to the multipath signal reflection problem.
-E-OTD is a handset based position estimation technique.
+on the location of the MS \citep{malik2009rtls}. This method is can still be susceptible to the multipath signal problem, however.
+E-OTD is a handset-based position estimation technique.
UL-TDOA (Up-Link Time Difference of Arrival) is a similar localization technique as E-OTD \citep{malik2009rtls}.
The basic difference between UL-TDOA and E-OTD is that the signal propagation time is observed on the BTS's and
not on the MS itself. To estimate the position of the MS, the BTS responsible for the MS forces the MS to request
-for a handover to neighboring two or more BTS's. The MS sends a handover burst signal and the neighboring BTS
+a handover to two or more BTS's nearby. The MS sends a handover burst signal and the neighboring BTS's
measure the waiting time between the handover request signal itself and the transmitted burst from the MS.
-Using the observed time difference, the BTS's can compute the location of the MS. It is important to note, this
+Using the observed time difference, the BTS's can compute the location of the MS. It is important to note that this
position estimation technique takes place while there is an active call on the MS or the BTS makes a silent call
to the MS where the mobile user is not aware of being tracked \citep{malik2009rtls}. This technique is slightly
-less accure than E-OTD, the accuracy lies between 50-300 m \citep{200mRangeEOTD}. Both of these techniques are
-challenged by the nature of the GSM network due to its unsynchronized operation. One microsecond error shall produce
+less accure than E-OTD; the accuracy lies between 50-300 m \citep{200mRangeEOTD}. The unsynchronized operation of
+the GSM network makes these two techniques impossible without clock synchronization. One microsecond error would produce
an error of around 300 m. The advantage of UL-TDOA over E-OTD lies in the fact that no extra software modifications
-have to be made on the cell phone and this technique works on every cell phone. UL-TDOA is a network based position
+have to be made to the cell phone and this technique works on every cell phone. UL-TDOA is a network-based position
estimation technique.
\subsection{Assisted-GPS}
-Another positioning technique named Assisted-GPS (AGPS) is recently gaining on popularity
-because of the great number of smart phones with an embedded AGPS receiver and the introduction.
-of 3G/4G networks. These networks are clock synchronized since
+Another positioning technique is Assisted-GPS (AGPS). It has recently gained popularity
+because of the great number of smart phones with an embedded AGPS receiver and the introduction
+of 3G/4G networks. These networks are clock-synchronized since
high-bandwidth wireless services require synchronous working operation \citep{oscilloquartz} \citep{3gNetworkSpeed}.
AGPS receivers can decrease the waiting time required to estimate the position if the
``exact'' time is known \citep[Chapter 4]{diggelen2009a-gps}.
It works by exploiting the existing
navigation satellite network.
-In the case when mobile users are in urban environments, the GPS satellite signals are blocked
-by the buildings. Further analyses showed that the received signals, at the cell phone arrive
-with errors because of multiple propagation reflection and are mostly hard
+In the event where mobile users are in urban environments, the GPS satellite signals are blocked
+by the buildings. Further analyses showed that the received signals arrive at the cell phone
+with errors because of multiple propagation reflection and are often hardly
distinguishable from noise \citep[Chapter 2]{diggelen2009a-gps}.
The power of received signals on a GPS receiver is in the range
of 100 attowatts\footnote{1 attowatt = $10^{-16} W$.
-The reception quality depends on the receiver antenna and RF front-end part as well.}
-when the GPS receiver is outdoors on open sky,
-the signal strength becomes even smaller by a factor of 10-1000 if the user is
-between tall buildings or indoors \citep[Chapter 2]{diggelen2009a-gps}. All these given factors
+The reception quality depends on the receiver's antenna and RF front-end design as well.}
+when the GPS receiver is outdoors.
+The signal strength becomes even smaller by a factor of 10-1000 if the user is
+between tall buildings or indoors \citep[Chapter 2]{diggelen2009a-gps}. All these factors
affect the acquisition of GPS signals and make the correct reception of GPS signals unrealisable
and impractical.
Instead of searching manually for the GPS satellites and waiting
for the orbiting parameters to arrive from the satellites, which are required to estimate the
-position, information about the orbiting GPS satellites are transmitted over an existing GSM
+position, information about the orbiting GPS satellites is transmitted over an existing GSM
network infrastructure. This provides the AGPS receiver additional data to track weak signals.
The theoretical foundation of how GPS and AGPS receivers estimate the position is addressed
-in more detail in chatper \ref{gpsTheoryChatper}.
-This method does not work on every cell phone as the previously mentioned methods.
+in more detail in chapter \ref{gpsTheoryChatper}.
+This method does not work on every cell phone as do the aforementioned methods.
It requires the cell phones to be equiped with an AGPS receiver.
-From this point on, cell phones with an AGPS receiver shall be refered as smart phones
+From this point on, cell phones with an AGPS receiver shall be refered to as smart phones
since they have another potential use aside from the default communication application. The AGPS
-position estimation technique is a hybrid based technique because the position is estimated
+position estimation technique is a hybrid-based technique because the position is estimated
with the help of the handset, that estimates the position, and the network provider since
it delivers the required data for faster acquisition time.
\subsection{Other techniques}
-The earlier mentioned localization techniques are not the only existing methods but are the standardized ones.
-In this section, two more techniques shall be briefly described, angle of arrival and Google maps WiFi tagging.
+The previously-mentioned localization techniques are not the only existing methods but are the standardized ones.
+In this section, two more techniques shall be briefly described: Angle-of-Arrival and Google Maps' WiFi tagging.
\begin{figure}[ht!]
\centering
\includegraphics[scale=1.20]{img/AOA.pdf}
- \caption{Basic idea of the Angle of Arrival positioning technique. The angle of the reception signal
+ \caption{Basic idea of the Angle-of-Arrival positioning technique. The angle of the reception signal
on the BTS antenna is measured. By knowing at least two angles on two BTS's, it is possible to
interpolate the intersection point where the MS is located.}
\label{img:aoadLoc}
\end{figure}
-Angle of Arrival (AOA) is a localization technique that exploits a geometric fact that by knowing at least
+Angle-of-Arrival (AOA) is a localization technique that exploits a geometric fact that by knowing at least
two angles from two known points, i.e. BTS's, it is possible to construct the third triangle point (intersection point).
The intersection point represents the location of the MS. The angle is derived by a burst
signal transmitted from the MS and the time difference of arrival for different elements of the burst
@@ -243,13 +244,13 @@ position estimation techniques.
\label{img:WiFiTag}
\end{figure}
-Another technique gaining on popularity is used by Google maps to identify the position of the user by
+Another technique gaining in popularity is used by Google Maps to identify the position of the user by
simply tagging an area with all visible wireless access points \citep{googleLBS}. Since each access point has a unique MAC address
it is not hard to identify them while driving through urban areas with a WiFi scanning device. The basic idea is
depicted in figure \ref{img:WiFiTag}, where the MS in this particular example is located where access points
1, 2 and 4 are visible at the same time stamp.
This technique works efficiently indoors as well as outdoors in cities since
-ranges of wireless networks 801.11 b/g are not more than 30-150 m, though the new standard 801.11 n has a wider coverage area.
+ranges of 801.11 b/g wireless networks are not more than 30-150 m, though the new standard 801.11 n has a wider coverage area.
A simple overview of all the discussed techniques is given in
table \ref{tbl:overviewLoc}.
@@ -296,37 +297,35 @@ background knowledge required for building a localization system of mobile users
inside of a 2G GSM network by taking the advantage of AGPS receivers inside of smart phones.
%This work may be perceived as pioneer work from authors perspective
-The thesis can be divided into three parts, theoretical introduction to GSM and GPS systems as well as
-the protocol required for the positioning of mobile users. The second part shall provide more details on
-the software implementation and the hardware used in this work. The last part may be seen as a discussion
-of the achieved results in the test environment and authors views on the work.
+The thesis is divided into three parts. The first is a theoretical introduction to GSM and GPS systems as well as
+the protocol required for the positioning of mobile users. The second part provides more details on
+the software implementation and the hardware used in this work. The last section is a discussion
+of the achieved results in the test environment and the author's conclusions.
-Theoretical knowledge of GPS and AGPS receivers shall be provided in chapter 2,
-as well as of the GSM operational principles in chapter 3 for understanding the basic functioning principles of the
+Chapters 2 and 3 will provide a theoretical introduction of GPS and AGPS receivers
+as well as of the GSM operational principles for understanding the basic functioning principles of the
entire positioning system. The theoretical concepts of GPS receivers
-shall be analysed and discussed in profound depth
-since it shall provide strong evidence on the advantages and limitations
-of this method. These two chapters shall provide an answer for the achieved
+will be analysed and discussed in depth
+since they provide evidence for the advantages and limitations
+of this method. These two chapters will provide an explanation for the achieved
and observed results in this thesis. Once the GPS and GSM working principles have
been explained, the author shall proceed with introducing the reader to the
Radio Resource Location Protocol (RRLP), responsible for transmission of
assistance data and obtaining the position of the mobile user. More
-details on RRLP shall be given in chapter 4.
+details on RRLP will be provided in chapter 4.
-Furthermore, the reader shall be introduced to the software
-development and implementation process in chapter 5. More details on the hardware connections and set up
+In chapter 5, the reader will be introduced to the software
+development and implementation process. More details on the hardware connections and set up
shall be provided in chapter 6.
-In the last two chapters of this thesis, in chapter 7 test results shall be presented and the test environment.
-In chapter 8 summary of the entire system shall be provided.
+In chapter 7 test results and the test environment will be presented.
+Chapter 8 will provide a summary of the entire system.
-In the appendix, details for configuring the entire system and for obtaining the same results
-shall be provided. This thesis includes an USB stick with the source code developed
+The appendix contains details for configuring the entire system and for obtaining the same results.
+This thesis includes a USB stick with the source code developed
during the work on this thesis.
-
-
\setchapterpreamble[u]{%
\dictum[Stobaeus] {What use is knowledge if there is no understanding?}
}
@@ -1634,6 +1633,7 @@ radio link control messages (signal strength and synchronization data) on the SA
\chapter{Radio Resource Location Protocol}
+\label{rrlpChapt}
This chapter shall focus on the Radio Resource Location Protocol (RRLP) and a description
how it works inside of the GSM network shall be given. RRLP is a protocol from the family of Location Services (LCS)
which were not part of the initial GSM standard. It is a widely used protocol in other cellular
@@ -2605,7 +2605,7 @@ procedures for creating a data channel between the BTS and MS. This channel
was deployed for the transmission of assistance data to the MS and for obtaining
the response from the MS.
-\section{Initial phase of trying out RRLP}
+\section{Initial phase}
Traditionally all radio communication systems are hard wired and
the hardware is developed to do only one fixed function as the
nanoBTS, to serve as a BTS. nanoBTS is a dedicated BTS hardware,
@@ -2677,41 +2677,7 @@ the RRLP protocol. The generated assistance data packets by the module were used
for comparison and a template to build author's RRLP assistance data generator. The nanoBTS
is operated by OpenBSC which is explained in the following section.
-\section{RRLP assistance data generator application}
-At the point, two different RRLP implementations on two different hardware platforms have been tested
-without successfully obtaining a GPS localization.
-\ref{img:RRLPAlgFlowchart}
-In this work two programming languages have been employed, C and C++
-whereas basic knowledge of Erlang was required to understand an implementation of a similar RRLP assistance
-data generation. The Erlang implementation by Kurtis Heimerl was used as a guide while the author
-developed a C++ version since at the time of testing it was not a working implementation of the RRLP
-protocol\footnote{Kurtis Heimerl's
-code can be found on \url{https://github.com/ttsou/RRLP}}! More details shall be given in the following
-sections. OpenBSC is an open source implementation of
-
-
-\begin{figure}[hb]
- \centering
- \includegraphics[scale=0.39]{img/algorithmRRLP.pdf}
- \caption{Flowchart for the RRLP assistance data generators}
-\label{img:RRLPAlgFlowchart}
-\end{figure}
-
--from rinex conversion\\
-explain rinex form \\
-explain a bit ephemeris data and almanac \\
-data and conversion \\
-
-Author's test system operated on the ARFCN 877 channel. ARFCN (Absolute Radio
-Frequency Channel Number) defines the uplink and downlink channel frequency insdide
-the GSM network \citep{Richard2011Master}. ARFCN 877 corresponds to the uplink frequency
-of 1,783.2 MHz and a downlink frequency of 1,878.2 MHz, where the uplink direction
-represents the direction from the nanoBTS to the mobile stations and downlink the
-opposite direction. The decision to use the ARFCN 877 channel was derived from
-the fact that the channel was free, measurements were carried out with a
-spectrum analyser built on the USRP hardware.
-
-\section{OpenBSC}
+\section{OpenBSC and its RRLP implementation}
OpenBSC is an open source implementation of a GSM network software by Osmocom.
It was developed for experimentation and security research of the GSM networks \citep{obsc1}.
OpenBSC is ``implementing the minimal necessary parts to build a small,
@@ -2741,6 +2707,83 @@ another approach had to be taken by the author to send RRLP assistance data
with position requests. This shall be further analysed and explained in more
details in the following sections.
+\section{RRLP assistance data generator}
+At the point of working on this thesis,
+two different RRLP implementations on two different hardware platforms
+have been examined without successfully obtaining a GPS localization.
+The next step in the attempt to obtain GPS positions from MS was to
+gain better understanding of the RRLP protocol and RRLP assistance data.
+The RRLP assistance data generated by Heimerl's application
+did not produce valid assistance data. In order to publish the RRLP assistance
+data generator as open source to be wider extended or ported to another
+programming language, it was required to be written in a programming language
+understandale by wider audience. It was sound to write the RRLP assistance
+data generator in C++ because OpenBSC was written in C and OpenBTS in C++.
+
+In the almanac
+and ephemeris files, downloaded from NASA and Trimble, assistance data were stored
+for 32 different GPS satellites. Contrary to expectations after the generated
+RRLP packets have been analysed, Heimerl's code produced RRLP assistance
+data packets with only valid data for one satellite but duplicated 32 times.
+At this stage, it was important to have a fully working RRLP assistance data
+generator. This generator would be subsequently used to examine the RRLP
+protocol once OpenBSC was modified to open a data channel for transmitting
+the assistance data with the RRLP position request. Heimerl's code, written
+in Erlang, had to be fully understood to build a working replica RRLP
+assistance data generator. It was used as a template with the specified RRLP
+conversion standard itself. The downloaded assistance data were
+in formats known as Receiver Independent Exchange format (RINEX) for ephemeris
+data and Yuma for almanac data. RINEX is a format to exchange raw satellite
+navigation data from GPS receivers that have an ability to output them.
+Although almanac data can be in RINEX form as well, the almanac data
+found online were in the Yuma format. The read files with assistance
+data had to be first properly parsed and then converted into the format
+specified in the standard by ETSI TS 144 031 \citep{ETSITS144031}.
+Once they were successfully parsed and converted, they had to be verified
+to be in the specified range as in the standard. Afterwards the converted
+and verified assistance data were combined into binary series of data
+according to the RRLP standard as described in chapter \ref{rrlpChapt}.
+If the assistance data packet size in binary format was not divisible by eight
+then additional padding zeros are added until this condition was satisfied.
+Better comprehension of the RRLP assistance data generator can be gained
+by looking at the flowchart in figure \ref{img:RRLPAlgFlowchart}.
+
+\begin{figure}[ht]
+ \centering
+ \includegraphics[scale=0.39]{img/algorithmRRLP.pdf}
+ \caption{Flowchart for the RRLP assistance data generators}
+\label{img:RRLPAlgFlowchart}
+\end{figure}
+
+Since the ephemeris data refresh every two hours, the latest generated data
+are appended at the end of the file for the current reading\footnote{This
+is performed by Trimble, whose ephemeris data were used.}.
+It was common that the ephemeris assistance data contained errors which
+were detected in the data range verification step. To avoid disruption
+in operation of the written software, once data out of range were detected
+they are immediatelly substituted with data for the same satellite
+but with two hours older ephemeris data. If the AGPS receiver in the MS uses
+the ephemeris data from that particular satellite then the distance estimation
+is affected and may contain errors! This problem is well known and confirmed
+by different studies \citep{Stanford-Ephem-Errors} \citep{NASA-Ephem-Errors}.
+A solution to this problem is proposed in the future work section. Once the
+assistance data have been generated and saved in a text file they can be used
+by OpenBSC to be transmitted to the MS.
+
+\section{Creating data channel in OpenBSC}
+
+
+%Author's test system operated on the ARFCN 877 channel. ARFCN (Absolute Radio
+%Frequency Channel Number) defines the uplink and downlink channel frequency insdide
+%the GSM network \citep{Richard2011Master}. ARFCN 877 corresponds to the uplink frequency
+%of 1,783.2 MHz and a downlink frequency of 1,878.2 MHz, where the uplink direction
+%represents the direction from the nanoBTS to the mobile stations and downlink the
+%opposite direction. The decision to use the ARFCN 877 channel was derived from
+%the fact that the channel was free, measurements were carried out with a
+%spectrum analyser built on the USRP hardware.
+
+
+
\chapter{Hardware}
In the following chapter the author shall introduce the reader to the hardware