This document discusses Assisted GPS (A-GPS) which enhances GPS performance on mobile devices. A-GPS uses cellular network elements to provide GPS data like satellite orbital information and rough location to help phones lock onto satellite signals faster indoors or in poor conditions. It works by the mobile network locating a phone roughly via cell tower and assisting with GPS calculations for a more precise location. The key components are the A-GPS terminal, gateway, server for assistance data and calculations, and database.

1. ASSISTED GPS (A-GPS) 簡介

2.  Conventional Standalone GPS
 Worked on 1575.42MHz and 1227.60MHz
 27 satellites were separated into 6 orbits on 20200km
height
 24 satellites for use
 3 satellites for spare
 At least 4 satellites to calculate position,
 3 to find out Lat/Long and height
 1 to synchronize
 GPS characteristics
 When first turned on
 Searching satellite -> Establish relation -> Receiving data ->
Calculation -> Result
 Poor signal conditions
 Surrounded by tall buildings (resulting in multi-path)
 The satellite signals are weakened when a GPS device is used
indoors or under trees.
GLOBAL POSITIONING SYSTEM (GPS)

3.  Mobile device receives the frame sent by satellite
 30 sec per frame
GLOBAL POSITIONING SYSTEM (GPS)

4.  Enhance the startup performance of a GPS satellite-
based positioning system
 Abbreviate TTFF (Time to First Fix)
 Enhance GPS sensitivity
 Indoor coverage
 A-GPS, using network elements such as either an
assistance server or other data from a network, falls
into two modes:
 MS based A-GPS
 MS Assisted A-GPS
ASSISTED GPS (A-GPS)

5.  Can locate the phone roughly by which cell site it is
connected to on the cellular network.
 Has a good satellite signal, and lots of computation
power, so it can compare fragmentary signals relayed
to it by cell phones, with the satellite signal it receives
directly, and then inform the cell phone or emergency
services of the cell phone's position.
 Can supply orbital data and almanac for the GPS
satellites to the cell phone, enabling the cell phone to
lock to the satellites faster.
 By having accurate, surveyed coordinates for the cell
site towers, it has better knowledge of ionospheric
conditions and other errors affecting the GPS signal
than the cell phone alone, enabling more precise
calculation of position.
ASSISTANCE SERVER

6.  A-GPS terminal device
 MS, A-GPS module
 GMLC
 Conversation gateway
 A-GPS server
 Web-based management
 Calculation
 GIS server
 Map information
 Database server:
 Location data
 POI
ASSISTED GPS SYSTEM STRUCTURE

7.  Coordinates of the TX antenna of the cell in WGS-84
format.
 Latitude: degrees (0, 90), minutes (0..59), seconds (0..59),
fractions (0..99), Latitude sign (0,1)
 Longitude: degrees (0, 180), minutes (0..59), seconds (0..59),
fractions (0..99), Longitude sign (0,1)
 Altitude: direction (height, depth), altitude measured from the
sea level to the TX antenna: meters (0..10000)
 ACOS(COS(RADIANS(90-Lat1))
*COS(RADIANS(90-Lat2)) +SIN(RADIANS(90-Lat1))
*SIN(RADIANS(90-Lat2)) *COS(RADIANS(Long1-
Long2))) *6371
 The greatest radius on an ellipsoid as 6378.135km
 The smallest as 6356.752km.
ASSISTED GPS DISTANCE CALCULATION