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} -- cgit v1.2.3-55-g7522