傳統GPS使用者接收器，必須先從人造衛星下載廣播星曆，下載導航資訊所需花費30秒。若下載完整導航資訊( Broadcast Ephemeris and Satellite Almanac ) 必須花費將近12.5分鐘；而藉由AGPS server架設GPS接收器，預先從衛星上下載廣播星曆，再藉由網路傳輸傳至使用者，縮短使用者第一次定位之時間( The time-to-first-fix, TTFF )，達到快速定位。
本研究中主要為利用IGS( International GNSS Service )提供之精密星曆與推導觀測量偏微分模型，透過最小平方法轉換成大眾較習慣之廣播星曆。其中觀測量偏微分模型為一複雜的數學推導，因此透過加入狀態誤差、觀測量誤差等，來驗證此模型。
比較轉換後廣播星曆與廣播星曆，分別計算位置並與精密星曆比較，可將原本最大14公尺的誤差降至0.8公尺內，且應用於導航中可得到與廣播星曆相似之結果，但使用者可以提前數個小時預收導航星曆，增加使用者便利性。

The traditional GPS receiver must download broadcast ephemeris from the satellites. Downloading the information for guidance will cost 30 seconds, which will cost approximate 12.5 minutes for download the entire guidance message. The AGPS method setups the GPS receiver through the AGPS server, that will download the broadcast ephemeris from the satellites beforehand. The AGPS server will pass the broadcast ephemeris on to the user receiver by the internet connection, which will reduces the time to first fix ( TTFF ), and achieves the fast navigation.
The primary method of this research is to use the precise ephemeris International GNSS Service, which provides and decides the observation Partial differential model to convert into a more useful broadcast ephemeris by using the Least-Squares method. The observation Partial differential model is a complex mathematics model. Therefore, the condition error, the observation error, and etc. will be added to prove the accuracy of the derived model.
Computing respectively of the satellite position is compared with using precise ephemeris and broadcast ephemeris that is able to decrease the maximum error from 14 meter to 0.8 meter. In addition, it has the same navigation result by using broadcast ephemeris, but the users can download this ephemeris several hours before they go outdoors. It could increase the convenience for the users as well.

[ 1 ] Elliott D. Kaplan, Christopher J. Hegarty(2005), Understanding GPS
Principles and Application, second Edition, ARTECH HOUSE, BOSTON. pp.1-3
[ 2 ] 曾清涼,儲慶美(1999), GPS衛星觀測原理與應用 第一版,
國立成功大學 衛星資訊研究中心. pp. 2-31 – 2-35
[ 3 ] Shaojun Feng, Choi Look Law(2002), Asissted GPS and Its Impact on Navigation in Intelligent Transportation Systems,
the IEEE 5th international Conference on Intelligent Transportation Systems 3-6 , Singapore. pp.926-931
[ 4 ] 楊聿銘(2001) , 利用GPS建立自動航空照相, 碩士論文,
國立成功大學航空太空工程研究所, 台南. pp.3
[ 5 ] 何慶雄,翁錦堂,景國恩, GPS衛星精密軌道計算,
國立成功大學航太系. 國立成功大學衛星資訊中心
pp.2-3
[ 6 ] Navigation center(1993), ICD-GPS-200, IRN-200C-004,
From http://www.navcen.uscg.gov/ (2008/11/20)
pp.97-100
[ 7 ] Ching-Shun Ho, Jin-Zhong Chen, Chin-Tang Weng (1997)，
Precise Velocity Determination with GPS Doppler Measurements. Dept. of Aeronautics and Astronautics.
National Cheng Kung University. Tainan, Taiwan. pp.5

[ 8 ] Arthur Gelb, Joseph F. Kasper Jr. , Raymond A. Nash Jr., Charles F. Price, APPLIED OPTIMAL ESTIMATION , THE M.I.T. PRESS,
Massachusetts Institute of Technology Cambridge, Massachusetts, and London, England pp.23-24 pp.71-80 pp.102-107
[ 9 ] Guochang Xu(2007)， GPS theory、Algorithms and Applications 2nd ed.. Springer . pp.248-249
[ 10 ] Philip G. Mattos (2008)， Self-Assisted GPS, Sep 1, 2008,
GPS world
[ 11 ] Lionel Garin, SaiPradeep Venkatraman, Pramod Gupta(2007)，
A Novel Ephemeris Extension Compaction/ Decompaction method,
Proceedings of the 63rd Annual Meeting April 23 - 25
[ 12 ] Ching-Shun Ho (2007)，Optimal Filtering Theory and Its Applications handout. NCKU IAA. Unpublished manuscript.
[ 13 ] Shau-Shiun Jan (2007)，Satellite Navigation Modenrnizattion handout. NCKU IAA. Unpublished manuscript.