summaryrefslogtreecommitdiffstats
path: root/vorlagen/thesis/src/kapitel_x.tex
diff options
context:
space:
mode:
Diffstat (limited to 'vorlagen/thesis/src/kapitel_x.tex')
-rw-r--r--vorlagen/thesis/src/kapitel_x.tex199
1 files changed, 170 insertions, 29 deletions
diff --git a/vorlagen/thesis/src/kapitel_x.tex b/vorlagen/thesis/src/kapitel_x.tex
index b99e64c..568e1b7 100644
--- a/vorlagen/thesis/src/kapitel_x.tex
+++ b/vorlagen/thesis/src/kapitel_x.tex
@@ -4,8 +4,10 @@ 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
rapid development it became possible to integrate a GPS receiver into almost every cell
-phone without dramatically and drastically increasing the price, physical size or weight of
-the cell phone. It is important to note, the number of wireless connections increased as well,
+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,
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,
@@ -13,38 +15,176 @@ whereas in the US and Canada this number is slightly higher, 46\% \citep{smartPh
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) has grown out of it and since then
+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
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 \citep{Bonanza}. New ideas and algorithms for tracking,
+companies and Global Industry Analysts project by 2015 a global market
+worth of \$21 USD billion ($\approx$ \euro17.142 billion) \citep{Bonanza}.
+New ideas and algorithms for tracking,
navigation solutions, safety, security, local business search and payments will emerge
from it as well as the new market that will emerge from the results of data mining
-user's movement \citep{Bonanza}. The Enhanced 911 (E911), an emergency service in the US for linking
+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}.
+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 to have LBS capability integrated
-in the system and better LBS accuracy than compared to GSM networks \citep{lteLocation}.
+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 will be discussed and analysed, Cell-ID, time of arival, angle of
-arival and GPS positioning. Then the author will proceed and describe the goals of his thesis.
+wireless networks will be presented and analysed, Cell-ID, time of arrival, angle of
+arrival and GPS positioning. Then the author will proceed and describe the goals of his thesis.
-\section{Related work}
-fit into small devices as smart \citep{Zeimpekis}
+
+\newpage
+\section{Positioning techniques}
+In this section related technologies for estimating the position of a mobile user will 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 network became more popular and mature compared to the initial GSM standard so
+the demands grew for diffent 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 will 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. 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, will be presented. First simple and then more advanced techniques
+will be presented in their order.
+
+\subsection{Cell-ID estimation technique}
+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}.
+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.
+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
+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.
+
+\begin{figure}[ht!]
+ \centering
+ \includegraphics[scale=0.70]{img/CellID.pdf}
+ \caption[]{Cell-ID position estimation technique where a mobile user can be connected to only one BTS.}
+\label{img:cellid}
+\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
+\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 acknowleded 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
+of the circle. 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.
+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 gets reflected from multiple buildings
+or other objects which adds extra 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
+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
+any type of cell phone.
+
+\subsection{Received Signal Strength estimation technique}
+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
+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.}
+\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
+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
+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
+the measurement have not been conducted \citep{Richard2011Master}.
+In the next step the probability
+distribution, the Bayes Theorem, is utilised to estimate the location of the MS
+by computing probabilities for all the points in the map. The precision of this method
+is limited to the amount of BTS in range and the manufacturer design of the RF front end
+in the cell phone. However, this method can be applied on any cell phone and does not
+require a smart phone. It is a network based estimation technique.
+
+\subsection{Enhanced Observed Time Difference estimation technique}
+
+\subsection{Assisted-GPS estimation technique}
+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
+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
+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 gets 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
+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
+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.
+It requires the cell phones to be equiped with an AGPS receiver.
+From this point on, cell phones with an AGPS receiver will be refered as smart phones
+since they have another potential use besides the default communication application. The AGPS
+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.
+
+\newpage
\section{Goals of the thesis}
-The goal of the following thesis is to:
-- implement the Radio Resource Location Protocol inside of OpenBSC, to the extent of
-delivering correct GPS assistance data to cell phone subscribers
-inside the GSM network
-- test the protocol on 5-10 different smart phones
-- describe and analyse the background processes taking place inside of the cell phone
+In this thesis the author will give an attempt to provide theoretical and practical
+background knowledge required for building a localization system inside of a 2G GSM network by
+taking the advantage of cell phones with AGPS receivers.
+Theoretical knowledge of GPS and AGPS receivers will be provided,
+as well as of the GSM system. The theoretical concepts of GPS receivers
+will be analysed and discussed in profound depth
+since it will provide strong evidence on the advantages and limitations
+of this method. This will provide the correlation for the observed results.
+Once the GPS and GSM working principles have been explained, the author will proceed with introducing the reader
+to the Radio Resource Location services Protocol (RRLP)\footnote{At this point RRLP can be seen as
+the connection point between the AGPS and GSM subsystems.}, responsible for obtaining the location
+and transmission of the assistance data to the cell phone. Furthermore, the reader will be introduced to
+the software development process and the hardware connection schemes will be provided.
+In the last part of this thesis, test results and summary of the entire system will be discussed.
@@ -53,6 +193,7 @@ inside the GSM network
\dictum[Stobaeus] {What use is knowledge if there is no understanding?}
}
\chapter{GPS \& Assisted-GPS}
+\label{gpsTheoryChatper}
\begin{figure}[ht!]
\centering
\includegraphics[scale=0.38]{img/satelliteRanges.pdf}
@@ -298,14 +439,14 @@ t=t_{SV}-\Delta t_{SV}
Nevertheless, the broadcast satellite time
information is not sufficient to estimate the precise
-time at the moment of the signal arival. Even though the signal
+time at the moment of the signal arrival. Even though the signal
arrives in approximately\footnote{Propagation time
depends on user and GPS satellite position.} $77 \, ms$,
the precision of the atomic clock is in the
range of 10 ns \citep[Chapter 2]{diggelen2009a-gps}.
Undoubtedly the signal propagation (travel)
time, denoted as $t_{prop}$, has to be taken into account.
-In that case, the exact time at the moment of arival is known,
+In that case, the exact time at the moment of arrival is known,
denoted as $t_{exact}$ and is given in equation \eqref{eq:exactTime}.
%The signal propagation time must be known to
%estimate the distance from the satellite
@@ -1024,14 +1165,14 @@ measurements \citep{pseudorangeError} \citep[Chapter 7]{understandGPS}.
\newpage
\section{Assisted GPS in Wireless networks}
\label{sec:agps}
-In the following paragraphs Assisted GPS (A-GPS) will be presented and how it works.
-A-GPS receivers work on a ``similar principle'' as warm/hot start on GPS receivers.
+In the following paragraphs Assisted GPS (AGPS) will be presented and how it works.
+AGPS receivers work on a ``similar principle'' as warm/hot start on GPS receivers.
Instead of loading the recently saved data from the EEPROM, an external
transfer medium is used to deliver the same type of information that are known
at a warm/hot start \citep{755159}, \citep{901174}, \citep{springerlink:10.1007/s10291-002-0028-0}.
In this work, the external transfer medium is air and the information are transfered using electromagnetic
waves. The existing GSM interface was utilised for the purpose of delivering the data to the smart phone
-with an A-GPS receiver. The basic scenario can be seen in figure \ref{img:agpsPrinciple}.
+with an AGPS receiver. The basic scenario can be seen in figure \ref{img:agpsPrinciple}.
The BTS station is connected to the global navigation satellite system (GNSS) server, which is directly
connected to the GPS reference station. The GPS reference station delivers the GNSS server exact time stamps,
@@ -1040,7 +1181,7 @@ approximate location, satellite health as well as clock corrections, ionospheric
\begin{figure}[ht!]
\centering
\includegraphics[scale=0.50]{img/A-GPS.pdf}
- \caption[]{Basic A-GPS principle}
+ \caption[]{Basic AGPS principle}
\label{img:agpsPrinciple}
\end{figure}
@@ -1048,8 +1189,8 @@ Time stamp is not used in GSM networks since it can be
off by several seconds and would require additional equipment for synchronizing the network
\citep{springerlink:10.1007/s10291-002-0028-0}, \citep{901174}. However in CDMA networks the time stamp is
accurate to within $100 \, \mu s$ \citep{springerlink:10.1007/s10291-002-0028-0}. Approximate
-location is typically taken to be the location of the BTS from which the target A-GPS receiver
-acquires the assistance data. Ephemeris and navigation data obtained by the A-GPS receiver in the smart phone
+location is typically taken to be the location of the BTS from which the target AGPS receiver
+acquires the assistance data. Ephemeris and navigation data obtained by the AGPS receiver in the smart phone
help it to estimate the positions of the GPS satellites. This method can greatly
enhance the sensitivity of the receiver especially in urban environments \citep{springerlink:10.1007/s10291-002-0028-0}.
@@ -1062,9 +1203,9 @@ an antenna with a gain of $3\, \mathrm{dB}$ with respect to an isotropic (omnidi
\citep[Chapter 2]{diggelen2009a-gps}.} (located near ground) at worst normal orientation''
\citep{GPS-Interface-Specification}.
-A simplified A-GPS algorithm given in \citep{springerlink:10.1007/s10291-002-0028-0} will be presented here. This
+A simplified AGPS algorithm given in \citep{springerlink:10.1007/s10291-002-0028-0} will be presented here. This
algorithm benefits in speed the more assistance data is present. As the first satellites are tracked,
-the A-GPS algorithm has an estimation of the feasible region where the target A-GPS user might be located.
+the AGPS algorithm has an estimation of the feasible region where the target AGPS user might be located.
Consequently, this feasible region will shrink until the location has been fully estimated
\citep{springerlink:10.1007/s10291-002-0028-0}.
\begin{enumerate}[(i)]
@@ -1074,9 +1215,9 @@ Consequently, this feasible region will shrink until the location has been fully
\item Pseudoranges are calculated for each visible satellite $SV_i$.
\item Triangulate the position out of the pseudoranges $\rho_i$.
\end{enumerate}
-Although the A-GPS algorithms can be seen as a set of equations, with more unknowns terms known it is
+Although the AGPS algorithms can be seen as a set of equations, with more unknowns terms known it is
straightforward to solve the set of equations. However, with more of the unknown terms it takes more
-time to get (decode) them from the satellite messages. One should know various A-GPS algorithms exist,
+time to get (decode) them from the satellite messages. One should know various AGPS algorithms exist,
some do not require the exact time component and navigation data to be present in the assistance data
\citep{998892}.