All iPads Why is GPS and Cellular combined and not seperate?

PracticalMac said:

A number of Android tablets have GPS without Cellular.
So why is Apple forcing you to get Cellular if you just want GPS?

Some guesses I have is:
Shared antennas.
Cellular (Qualcomm?) chip includes both functions.
A-GPS (using cellular to quickly download updated satellite data)

or all of the above?


Also a ? about A-GPS,
does one get the satellite data even if you do not subscribe to cellular service???

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Or it's just marketing. You want GPS pay the extra $100

It's combined because its the same SOC; System-On-A-Chip is a sigle component.

A-GPS is just like regular GPS but it is assisted by cell towers and wifi networks to find your location quicker. The A doesn't mean they are downloading data, it just means the cell-towers triangulate your position quicker.

PracticalMac said:

Also a ? about A-GPS,
does one get the satellite data even if you do not subscribe to cellular service???

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You're not really getting "satellite data". The signal from the GPS satellites is just used to determine location. If it's not using the GPS satellites to determine your location then it's not GPS whether it's standalone or aGPS. Most aGPS receivers can fall back on standalone mode if the Ephemeris data isn't available from the assistance servers for whatever reason.

PracticalMac said:

AGPS might use the signal quality measurements off *a* single tower, but it does not triangulate.

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That's not entirely correct. It doesn't use cell tower triangulation but GPS is basically triangulation.

I've read some data from the cell towers is downloaded to more quickly establish location of satellites, so it can use some data. I need a reference though.

That's certainly the reason it's true in the iPad - no dedicated GPS chip. Any other answers are Apple business decision speculation.

darngooddesign said:

It's combined because its the same SOC; System-On-A-Chip is a sigle component.

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The wireless module is neither part of the SoC nor is it what you would generally classify as a system on a chip. The module does not function on its own. You might get away with 'ASIC' if you need a label.

PracticalMac said:

According to Wiki on ephemeris, it does actually download data from satellites.

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It listens for, receives, and inteprets data from satellites, but to call that a "download" in the sense it is usually understood isn't really common usage, just like you don't generally say that your TV "downloads" broadcast transmissions.

And yes to be accurate, triangulation is done by satellites, not cell towers.

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The triangulation is actually done in the receiver, to be accurate. Neither the cell tower nor the satellite actually interacts with the phone for location purposes.

PracticalMac said:

I think it is because of the SoC in the RTR8600 one gets "aGPS" (AGPS)

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It's not the SoC; it's the fact that the package is part of the integrated logic. Almost every device with GPS and cellular data connectivity uses aGPS in some capacity--it would be foolish not to take advantage of that.

cheaper to used a combined system then separate chips.

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Cheaper, less redundant, more space-efficient, more power-efficient, and better integrated into a mobile device.

The standalone GPS chips that you might find in a TomTom or Magellan GPS are not really suitable for a mobile device.

Anonymous Freak said:

That's certainly the reason it's true in the iPad - no dedicated GPS chip. Any other answers are Apple business decision speculation.

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Simple, concise, and accurate.

Clearly you do not belong on the Internet.

PracticalMac said:

Excellent details, thanks!

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No problem!

It sounds like the GPS will "build" a library of data listening to the satellites.

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Not a persistent library. GPS satellites constantly broadcast a bunch of information, but it's only one way. The satellites constantly tell you where they are and what time it is, with an extreme amount of precision. It doesn't do any good for the GPS receiver to log data into a historical library--all of the satellite data is basically useless once it's transmitted, except for certain details that only change every few hours or days.

The receiver listens to that data and compares the timestamp of the satellite to the time when the message is received. Knowing the location of the satellite and how long it took to receive the signal tells you where you are on the planet.

It takes a comparatively long time to listen for long enough to get all the location information from the satellite, because it is a fairly low bandwidth transmission. That's where assisted GPS comes in.

But for Assisted, does it instead receive a file of like data?

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Radio transmissions from the satellites are slow. Terrestrial radio transmissions, even on relatively bandwidth-constrained 2G/3G networks, is much faster. In a nutshell, assisted GPS gets data on the location of GPS satellites from cell towers or other sources, rather than waiting for the complete set of data on the slow satellite signal.

That's what makes it faster to find your location with aGPS.

I also assume if in with Wi-Fi connection to internet it will also download the data (as in Cell is turned off).

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That depends on the specific GPS hardware and software in your device. Some get their data over the Internet and some get it only from the cell towers.

ActionableMango said:

Simple, concise, and accurate.

Clearly you do not belong on the Internet.

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That's the first time that has been said about me.

Uh......

Thanks?