From 472be2cb01f49511a9938aceeaff902df6b5aad1 Mon Sep 17 00:00:00 2001
From: Refik Hadzialic
Date: Thu, 21 Jun 2012 18:54:55 +0200
Subject: Writing A-GPS and distance estimation

---
 vorlagen/thesis/src/kapitel_x.tex | 77 +++++++++++++++++++++++++++++++--------
 1 file changed, 62 insertions(+), 15 deletions(-)

(limited to 'vorlagen/thesis/src/kapitel_x.tex')

diff --git a/vorlagen/thesis/src/kapitel_x.tex b/vorlagen/thesis/src/kapitel_x.tex
index ad939fd..5adca42 100644
--- a/vorlagen/thesis/src/kapitel_x.tex
+++ b/vorlagen/thesis/src/kapitel_x.tex
@@ -381,7 +381,10 @@ further explained in the following section \ref{sec:2dSearch}.
 
 \subsection{Implementation of the 2D search space problem}
 \label{sec:2dSearch}
-As it can be seen, from subsections \ref{sec:CAdemod} and
+In the following paragraphs an introduction will be given on 
+the implementation problems of the previously mentioned concepts. 
+As it can be seen, 
+from subsections \ref{sec:CAdemod} and
 \ref{sec:Carrierdemod}, decoding the GPS navigation message is a 2D 
 search space problem for each GPS satellite
 signal acquisition. The 2D search space is limited by well known
@@ -471,27 +474,71 @@ The speed of searching the 2D search space (finding the peak)
 depends on the complexity and strategy of the 
 implemented algorithm \citep[Chapter 6]{9780817643904}. In the worst case,
 there are in total 102300 conbinations in the search space,
-this can be derived from equation \eqref{eq:totalSearch}.
+this can be derived from equation \eqref{eq:totalSearch}, visually shown 
+in figure \ref{img:SearchSpace2d}.
 \begin{equation}
 \label{eq:totalSearch}
 \mathrm{Search \, Space} = 50 \,\mathrm{(bins)} \cdot 1023\, \mathrm{(C/A \,codes)} \cdot 2\, \mathrm{(Phases\, per\, C/A\, chip)}
 \end{equation}
-The common strategy is to start searching from the middle frequency bin,
-first 500 Hz, second -500 Hz, then 1000 Hz and -1000 Hz until the entire
-search space has been exhausted \citep[Chapter 3]{diggelen2009a-gps}. 
-This search space can be reduced by changing the sensitivity of the GPS receiver with the already given 
-equation \eqref{eq:mistunigLoss} or delivering required information to the GPS receiver like the frequency
-ranges, phase-shifts and etc. This method is also known as A-GPS \citep{755159} and will be further analysed
-in the following subsection. 
-
-\subsection{The A in A-GPS}
-After the peaks have been found for each seen satellite, it can
-receive the navigation messages and estimate the position.
-There are three different searching modes, if no information are known,
+\begin{figure}[ht!]
+  \centering
+  \includegraphics[scale=0.50]{img/2DSearchSpace.pdf}
+  \caption[]{The total search space}
+\label{img:SearchSpace2d}
+\end{figure}
+
+The common strategy is to start searching from the middle frequency bins and to jump
+up and down until the entire search space has been exhausted (first 500 Hz,
+second -500 Hz, then in the 1000 Hz bin and then in the -1000 Hz bin) 
+\citep[Chapter 3]{diggelen2009a-gps}.
+This procedure is performed when no extra information are known by the receiver, i.e. 
+first time the GPS receiver is turned on. It is known under the name of cold start.
+There are three different working mechanisms when it comes to searching
+for the GPS satellites. If no information are known,
 when some information are known and when almost all information are
-known. These three modes are known as cold, warm and hot start.
+known. These three modes are known as cold (as mentioned earlier),
+warm and hot start. They differ from each other by the amount of known
+information by the GPS receiver. Cold start indicates the GPS receiver
+has no almanac\footnote{Almanac information are rough estimation parameters for
+predicting the orbital position of the GPS satellites.}, ephemeris\footnote{Ephemeris
+information are precise parameters for predicting the orbital position of the GPS satellite.}, 
+oscillator offset and time data. In order to track the satellites faster next time
+the GPS receiver is started, it stores the previously mentioned data (last known almanac, 
+ephemeris, oscillator offset, time and position data) in its electrically erasable
+programmable read only memory (EEPROM). This type of start is known as a warm start,
+provided that the data in the receivers' EEPROM are not older than 180 days and
+its real time clock counter was constantly updated.
+In this case, the receiver uses the previously saved information
+to estimate the position of the satellites, therefore the Doppler effects can be estimated. 
+As a consequence of the known Doppler effect, the frequency bin where to start
+the search first is known as well \citep[Chapter 3]{diggelen2009a-gps}.
+In the same way works the hot start, only the time is precisely
+known in accuracy of submilliseconds. 
+
 \section{Distance and position estimation}
 
+\section{Assisted GPS}
+\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.
+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 the A-GPS receiver.
+
+The BTS station is connected to the GNSS server, which is directly
+connected to the GPS reference station and .
+
+\begin{figure}[ht!]
+  \centering
+  \includegraphics[scale=0.50]{img/A-GPS.pdf}
+  \caption[]{Basic A-GPS principle}
+\label{img:agpsPrinciple}
+\end{figure}
+
+
 \chapter{Radio Resource Location Protocol}
 
 \chapter {Working}
-- 
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