All About Symbian - Nokia (S60) and Sony Ericsson (UIQ) smartphones unwrapped

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Old 16-10-2007, 05:43 PM
justnew justnew is offline
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GPS & Internet

I have a question which you may find it wiered but the reason I'm asking is I don't have enough background with GPS technology, so ... the question, GPS signal comes from the satellite and there are some satellites can provide internet, so is that mean using the GPS receiver you can (one day ) get also internet connection

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Old 16-10-2007, 06:12 PM
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kontraband kontraband is offline
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I dont really have a knowledge of it either , but, a GPS satellite works along with at least 2 other satellites to triangulate your position. Why would that then become a method of receiving Internet packets? I woudnt imagine the infrastructure is anywhere near enough to support that amount of data?

Last edited by kontraband; 16-10-2007 at 09:07 PM. Reason: because my spelling sucked!

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Old 16-10-2007, 07:23 PM
justnew justnew is offline
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make sense

Quote:
Originally Posted by kontraband View Post
I dont really have a knowledge of it either , but, a GPS satellite works along with at least 2 other satellites to triangulate your position. Why would that then become a method of recieving Internet packets? I woudnt imagine the infrastructure is anywhere near enought to support that amount of data?

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Old 16-10-2007, 11:32 PM
argh argh is offline
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Some satellites can be used to provide an internet connection, but importantly they need a reasonable size satellite dish to get a good quality signal (there are telephones that can communicate directly to satellites - useful when you are out in the middle of nowhere).

Even more importantly, the GPS satellites do not receive anything from your phone, all the information is from the satellite to your phone. I'm not sure that I'd be very interested in not being able to pick which web pages I received

For this reason, you are more likely to see a phone picking up satellite radio or TV transmissions than anything interactive. I'm not sure about satellite radio, but I think that most video streams would require some sort of external dish to get the required data rate.

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Old 17-10-2007, 01:02 AM
canadian* canadian* is offline
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Gps 101

What is it ..

The Global Positioning System (GPS) is the only fully functional Global Navigation Satellite System (GNSS). Utilizing a constellation of at least 24 medium Earth orbit satellites that transmit precise microwave signals, the system enables a GPS receiver to determine its location, speed/direction, and time.

Developed by the United States Department of Defense, it is officially named NAVSTAR GPS (Contrary to popular belief, NAVSTAR is not an acronym, but simply a name given by Mr. John Walsh, a key decision maker when it came to the budget for the GPS program.

The satellite constellation is managed by the United States Air Force 50th Space Wing. The cost of maintaining the system is approximately US$750 million per year,[2] including the replacement of aging satellites, and research and development. Despite these costs, GPS is free for civilian use as a public good.

Pickup

A GPS receiver calculates its position by measuring the distance between itself and three or more GPS satellites. Measuring the time delay between transmission and reception of each GPS microwave signal gives the distance to each satellite, since the signal travels at a known speed near the speed of light. These signals also carry information about the satellites' location and general system health (known as almanac and ephemeris data). By determining the position of, and distance to, at least three satellites, the receiver can compute its position using trilateration.[3] Receivers typically do not have perfectly accurate clocks and therefore track one or more additional satellites, using their atomic clocks to correct the receiver's own clock error.

Chipset

* SIRF 3 - The SiRFstarIII chip is distinguished from earlier SiRF chips and from GPS chipsets made by other manufacturers (Garmin or Trimble for example), largely due to its faster Time to First Fix (TTFF) and its ability to acquire and maintain a signal lock in urban or densely covered forest environments. The enhanced abilities of the SiRFstarIII chips are made possible by several features. The chip supports 20 parallel channels, meaning that the chip can listen to, or search for, the signals from 20 different GPS satellites simultaneously. However, the current GPS system typically peaks at 12 satellites visible from one location plus a maximum of four WAAS satellites.
The chip consumes somewhat more power than SIRFstar II.
The chip can also make use of Assisted GPS to reduce the time needed to calculate its location. This feature makes the chip useful for cell phone manufacturers who want or need to support location services (such as the E911 legislation in the United States).

* High Sensitivity GPS - High Sensitivity GPS receivers use large banks of correlators and digital signal processing to search for GPS signals very quickly. This results in very fast times to first fix when the signals are at their normal levels, for example outdoors. When GPS signals are weak, for example indoors, the extra processing power can be used to integrate weak signals to the point where they can be used to provide a position or timing solution.

GPS signals are already very weak when they arrive at the Earth’s surface. The GPS satellites have transmitters that only deliver 27 Watts from a distance of 20,200km in orbit above the Earth. By the time the signals arrive at the users receiver they are typically as weak as –160dBW, equivalent to one tenth of a millionth billionth of a Watt. This is well below the thermal noise level in its bandwidth. Outdoors GPS signals are typically around the -155dBW level.

Conventional GPS receivers integrate the received GPS signals for the same amount of time as the duration of a complete C/A code cycle which is 1ms. This results in the ability to acquire and track signals down to around the -160dBW level. High Sensitivity GPS receivers are able to integrate the incoming signals for up to 1,000 times longer than this and therefore acquire signals up to 1,000 times weaker. A good High Sensitivity GPS receiver can acquire signals down to -185dBW, and tracking can be continued down to levels approaching -190dBW.

High Sensitivity GPS can provide positioning in many but not all indoor locations. Signals are either heavily attenuated by the building materials or reflected in as multipath. Given that High Sensitivity GPS receivers may be up to 30dB more sensitive this is sufficient to track through 3 layers of dry bricks or up to 20cm of steel reinforced concrete for example.

the N95 has a chipset equivalent to SirfStar 2

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Old 17-10-2007, 12:03 PM
waxup waxup is offline
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Quote:
Originally Posted by kontraband View Post
but, a GPS satellite works along with at least 2 other satellites to triangulate your position.
as canadian* pointed out:
GPS does not use Triangulation, it uses trilateration and does need atleast 3 reference points.

Trilateration is a method of determining the relative positions of objects using the geometry of triangles in a similar fashion as triangulation. Unlike triangulation, which uses angle measurements (together with at least one known distance) to calculate the subject's location, trilateration uses the known locations of two or more reference points, and the measured distance between the subject and each reference point. To accurately and uniquely determine the relative location of a point on a 2D plane using trilateration alone, generally at least 3 reference points are needed.

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Old 17-10-2007, 03:03 PM
mrtn2104 mrtn2104 is offline
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I bet you wish you'd never asked now don't you?

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Old 17-10-2007, 04:31 PM
waxup waxup is offline
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Well the question has been answered. GPS communication is not the same as an internet connection via satellite would be. There is a much larger data throughput for internet and different hardware would be needed.

I'm sure one day though, this shall be possible to have access to the internet via satellite/cell phone communications. I will not rule that out.

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Old 17-10-2007, 08:13 PM
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Quote:
Originally Posted by waxup View Post
trilateration
Quote:
Originally Posted by canadian View Post
trilateration

trilateration not triangulation... got it.

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Old 18-10-2007, 12:36 AM
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Trilateration will give a fixed stationary location point.
However, TomTom state that a signal from four sats is needed for their system.
I wonder if this is due to the need for continualy moving point determination?
Anyway, sat internet relies on a fixed line link for upload and the sat for download. No reason why a cell link could not be used as the upload link. Interesting idea!
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Old 18-10-2007, 02:54 PM
Richard G Richard G is offline
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interesting post guys! from what i understoon GPS sats just beam out information and dont receive anything, so wouldnt be any use for data related stuff

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Old 18-10-2007, 03:11 PM
chrsfrwll chrsfrwll is offline
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Quote:
Originally Posted by pa49 View Post
However, TomTom state that a signal from four sats is needed for their system.
I wonder if this is due to the need for continualy moving point determination?
I thought the forth is only needed to ensure the clock is in sync. Once you're on the move, it should give you a position with only 3 sats.
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Old 18-10-2007, 03:11 PM
justnew justnew is offline
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based on what you said we may see one day an application which receive internet from the Sat and send data through GPRS which should be small data (upload).


Quote:
Originally Posted by Richard G View Post
interesting post guys! from what i understoon GPS sats just beam out information and dont receive anything, so wouldnt be any use for data related stuff

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Old 18-10-2007, 04:30 PM
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Quote:
Originally Posted by justnew View Post
based on what you said we may see one day an application which receive internet from the Sat and send data through GPRS which should be small data (upload).
With packet data over GPRS and HSDPA etc now hitting the multi megabyte range I severly doubt satelitte internet even with gprs upload will ever take off. Satelite bandwidth is expensive and requires a line of sight where as current mobile data methods dont and if you already require the latter then the cost issue pretty ouch rules it out
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