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authorRefik Hadzialic2012-07-28 13:57:05 +0200
committerRefik Hadzialic2012-07-28 13:57:05 +0200
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RRLP and assistance data
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\subsection{RRLP Assistance data}
\label{sec:rrlpassistance}
+Assistance data are of the most important value when it comes to RRLP response time.
+If the assistance data are present, the response time ought to be shorter since
+the AGPS receiver knows the orbital information of the satellites and the exact time
+which allows the AGPS to find immediatelly the Doppler frequency and phase shift of
+the visible GPS satellite. In the assistance data packets, same as in the request
+packet, one has to specify what type of information are included in the assistance data.
+In this thesis, as assistance data only the almanac, ephemeris, UTC model, ionospheric
+model and reference location is transmitted to the MS. There are also other assistance
+data like differential GPS corrections (DGPS), real time integrity and reference time
+but none of these were available to the author, so they were avoided. The reasons for
+this decision were explained earlier as cost and complexity issues.
+
+DGPS corrections give additional accuracy to the GPS measurement reports between $1-3$ m \citep{489522} and they
+are rarely used \citep[Chapter 4]{harper2010server-side}. Real
+time integrity is a list of satellites the AGPS receiver ought not use because these satellites
+have an integrity problems \citep[Chapter 4]{harper2010server-side}.
+This helps the AGPS receiver to know why assistance data for satellites with errors
+are not included in the ephemeris or almanac and to be aware not to use instead the old
+cached data \citep[Chapter 4]{harper2010server-side}. Reference time can be considered as
+the ``most valuable'' data for the MS because it provides ``exact time'' to the AGPS receiver.
+This helps the AGPS receiver to better estimate the phase shift required to detect GPS
+signal which in return allows the AGPS receiver better integration period $\tau$ to detect
+weaker signals in cities or buildings (see section \ref{sec:SigDemod}
+and page \pageref{sec:CAdemod} for better understanding) \citep[Chapter 4]{harper2010server-side}.
+By knowing the reference time, it is straightforward for the AGPS receiver to predict the TLM and
+HOW starting words of the transmitted GPS packets from the satellites
+(refer to section \ref{sec:gpsDataAndSignal}). Reference time data can include the relationship
+between the GSM network and GPS time, as well as the GSM frame number to help the MS to
+synchronize with the BTS (earlier this was described as time synchronized GSM networks which is
+required for methods like E-OTD)\citep[Chapter 4]{harper2010server-side}.
+
+More information on assistance data transmitted inside the RRLP protocol will be presented now.
\newpage
\section{RRLP Response}