From d1debb5ca79aeba70671ba076984768c6ff5ebab Mon Sep 17 00:00:00 2001
From: Refik Hadzialic
Date: Sun, 24 Jun 2012 16:12:50 +0200
Subject: Writing about A-GPS

---
 vorlagen/thesis/src/kapitel_x.tex | 32 +++++++++++++++++++++++++++-----
 1 file changed, 27 insertions(+), 5 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 5adca42..6821449 100644
--- a/vorlagen/thesis/src/kapitel_x.tex
+++ b/vorlagen/thesis/src/kapitel_x.tex
@@ -251,7 +251,7 @@ The high frequency term, $(\omega_{1}+\omega_{2})$, can be filtered out using
 a low-pass filter\footnote{A low-pass filter passes
 low frequency signals and attenuates
 high frequency signals. In other words, signals higher than the
-speciefied cutoff frequency of the low-pass filter, are cut off by reducing their amplitudes.}.
+specified cutoff frequency of the low-pass filter, are cut off by reducing their amplitudes.}.
 Ideally, the difference of the angle frequencies is zero,
 as in equation \eqref{eq:delaOmega}, since $\cos(\Delta \omega)=\cos(0)=1$
 and the remaining left signal is only the C/A code multiplied
@@ -517,7 +517,7 @@ known in accuracy of submilliseconds.
 
 \section{Distance and position estimation}
 
-\section{Assisted GPS}
+\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.
@@ -526,11 +526,13 @@ 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.
+with the A-GPS receiver. The basic scenario can be seen in figure \ref{img:agpsPrinciple}.
 
-The BTS station is connected to the GNSS server, which is directly
-connected to the GPS reference station and .
+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,
+approximate location, satellite clock corrections, ephemeris and navigation data
 
+\citep{springerlink:10.1007/s10291-002-0028-0}. 
 \begin{figure}[ht!]
   \centering
   \includegraphics[scale=0.50]{img/A-GPS.pdf}
@@ -538,6 +540,26 @@ connected to the GPS reference station and .
 \label{img:agpsPrinciple}
 \end{figure}
 
+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 
+help it to estimate the positions of the satellites and they can greatly
+enhance the sensitivity of the receiver especially in urban environments \citep{springerlink:10.1007/s10291-002-0028-0}.
+
+Conventional GPS receivers require at least up to extra $18$ to $30\,s$ to receive and decode the navigation data
+and to generate a location fix \citep{springerlink:10.1007/s10291-002-0028-0}. 
+The bit error rate associated with gathering and decoding data dramatically decreases since the acquired signals 
+can be attenuated by $10$ to $20\, \mathrm{dB}$ indoors \citep{springerlink:10.1007/s10291-002-0028-0} of the nominal
+$-130 \,\mathrm{dB}$ on a $3\, dBi$ linearly polarized user receiving antenna\footnote{3 dBi antenna indicates
+an antenna with a gain of $3\, \mathrm{dB}$ with respect to an isotropic (omnidirectional) antenna
+\citep[Chapter 2]{diggelen2009a-gps}.} (located near ground) at worst normal orientation
+\citep{GPS-Interface-Specification}.
+
+
+
 
 \chapter{Radio Resource Location Protocol}
 
-- 
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