Server:A-GPS - Revision history

Kempelen: Category: -Technical, +GPS

2008-09-13T21:57:31Z

Category: -Technical, +GPS

Coolcat at 07:40, 3 September 2008

2008-09-03T07:40:37Z

Coolcat: /* What options are there for implementing an AGPS server? */

2008-09-03T07:40:20Z

‎What options are there for implementing an AGPS server?

Carcin: /* Fundamental GPS errors */ Added other sources of error, arranged by impact on accuracy of a typical reading

2008-04-28T07:30:49Z

‎Fundamental GPS errors: Added other sources of error, arranged by impact on accuracy of a typical reading

Speedevil: /* What options are there for implementing an AGPS server? */ add category

2007-08-31T12:26:19Z

‎What options are there for implementing an AGPS server?: add category

Speedevil: {{Unimplemented}}

2007-07-28T13:54:36Z

Glenn: -cat

2007-07-26T15:49:47Z

-cat

Speedevil: ad category

2007-07-24T16:25:25Z

ad category

Speedevil: Add first cut on page about an AGPS server for OpenMoko devices

2007-07-24T15:34:49Z

Add first cut on page about an AGPS server for OpenMoko devices

New page

=Why AGPS?=
Most conventional GPS recievers have difficulty providing reliable positions in environments surrounded by tall buildings - the so-called 'urban canyon', as well as indoors and under heavy tree cover.

Also, when initially turned on, there can be a significant delay before the receiver can provide a position.

The A-GPS server can help in both these cases, as well as providing additional functionality.

It is able to do this as:
*The Assistance Server 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 of its position.<small> Compare for example being asked to identify where a partially concealed known object is in a picture, and if you don't know what it is.</small>
*It can supply orbital data for the GPS satellites to the cell phone, enabling the cell phone to lock to the satellites when it otherwise could not, and autonomously calculate its position.
*It can have better knowledge of ionospheric conditions and other errors affecting the GPS signal than the cell phone alone, enabling more precise calculation of position.

==Fundamental GPS errors==
(approx, fixme!)

*Orbital error - 2m. These are inaccuracies in the orbits broadcast by the GPS satellites. Downloading precise orbits will fix this error, for a short time. This is a per-satellite error, but in practice, you'd download them all at once.
*Ionospheric error - 2m. This is due to the natural variation of the atmosphere. It varies moderately rapidly, and over several hundred kilometer areas. This error varies depending on the ionosphere that the satelite signal passes through to get to you.

==What options are there for implementing an AGPS server?==

All these require an open-source GPS driver. Or at least a more flexible binary one.

{|
|Simply provide for rapid download of accurate orbital data, in a compressed format.
|This is simple to implement, and provides modest gains in accuracy.
|-
|Compute position for phone
|Requires complex software to be written for the server
|-
|Supply ionospheric model to phone
|Relatively simple software on server, to echo internet sources of current ionospheric weather to the phone, opensource GPS driver on the phone.
|-
|Peer-Peer ionospheric model
|Use all stationary compatible phones with a view of the sky, and a free network connection to help derive an accurate ionospheric model. Also requires open-source GPS driver.
|}

[[Category:Server]]

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 =Why AGPS?=
 Most conventional GPS recievers have difficulty providing reliable positions in environments surrounded by tall buildings - the so-called 'urban canyon', as well as indoors and under heavy tree cover.
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← Older revision		Revision as of 16:25, 24 July 2007
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 (approx, fixme!)
-*Orbital error - 2m. These are inaccuracies in the orbits broadcast by  the GPS satellites. Downloading precise orbits will fix this error, for a short time. This is a per-satellite error, but in practice, you'd download them all at once.
+*Signal Resolution Error - 5m. A GPS receiver detects a signal transmitted by satellites and attempts to match that signal as closely as possible. The signal can only be matched to a given accuracy for the simple binary signal from the satellites. This is by far the largest error in the GPS system, and the easiest to detect.
 *Ionospheric error - 2m. This is due to the natural variation of the atmosphere. It varies moderately rapidly, and over several hundred kilometer areas. This error varies depending on the ionosphere that the satelite signal passes through to get to you.
 ==What options are there for implementing an AGPS server?==

← Older revision		Revision as of 13:54, 28 July 2007
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		+	{{Unimplemented}}
	=Why AGPS?=		=Why AGPS?=
	Most conventional GPS recievers have difficulty providing reliable positions in environments surrounded by tall buildings - the so-called 'urban canyon', as well as indoors and under heavy tree cover.		Most conventional GPS recievers have difficulty providing reliable positions in environments surrounded by tall buildings - the so-called 'urban canyon', as well as indoors and under heavy tree cover.