If you are looking to purchase a phone with a global position system, then you might have come across the terms GPS and aGPS. Is one better than the other? What are the differences? What do they mean and which one should I choose? These are just some of the questions that may have crossed your mind when thinking about it. Well for starters, it would be best to explain this from the ground up.

What Is GPS? 

Global Positioning Systems, or GPS as they are commonly called, allows you to track your location based on satellites. The GPS chip (be it a standalone GPS device or the your Pocket PC), will calculate you location based on the data it receives from the satellites. Thus, to triangulate your position, it would need a minimum of 3 satellites’ data (it is usually able to get a lot more anyway).

If your GPS chip has not been used in a long time, then the Time To First Fix (TTFF) can be a long time because it needs to download the data before it can make the calculations. If the chip was last used a couple of days ago, the time to fix may be shorter. This is usually referred to as a cold start. In cases when the chip was recently used (could be a couple of minutes or hours ago), the time to fix would be even faster. This would then be termed a warm start or a hot start.

Cold start, warm start and hot start are all relative and their definition varies from chip to chip (mainly due to marketing strategies more than anything). The reason why it takes so long is because unlike your broadband (or even dial up connections for that matter) the data transmission rate from these satellites is only 50bits per second. That’s just over 6 bytes per second. Which is why, it can sometimes take as long as 12 minutes (or even longer in some cases) to get a fix from a cold start as it has to download the data over a really narrow bandwidth. (I will stop the elaboration on bandwidth here but if you are interested, Wikipedia is a great read here).

So basically, that is what GPS is all about. Then what is aGPS?

Introduction To aGPS

aGPS means assisted GPS and you might guess what that means. It gets assistance to fix your location from other sources, usually cell towers. It is a newer version and as such, has some added features namely:

• ability to fix a location without a line of site to the satellites (which is required for traditional GPS).
• faster fix (because the data is already downloaded beforehand by the carrier).
• less processing power (because the carrier does most of the calculation for you).

Just based on these 3 factors alone, you might think that aGPS trumps GPS and that anyone who buys a GPS device when he has the option to choose aGPS must be nuts. Not really.

Advantages Of GPS

Unlike aGPS, you do need to rely on your carrier. So in the event where there is no network coverage, such as when you are in the jungle, or during times of natural disaster, your GPS chip will still be able to fix your position and you could use it navigate your way to safety or sought help.

GPS is also more accurate, when used with a highly sensitive chip like the SiRF Star III which can be found in the Eten Glofiish models. While this is more on a case by case basis (because you will get a better fix with aGPS when you are out in the open compared to the fix by the GPS when you are surrounded by tall structures), if you were to compare them side by side, most of the time, GPS would come out tops.

GPS Bridging The Gap

In addition, the Eten Glofiish devices has an application call Satellite Update whereby you can download the satellites data over the internet instead of doing it directly. This would significantly reduce the time to fix and is something which I practice. Before going out, I would always update the data such that when I step out, I get a fix within a minute, be it from cold or warm start. Hot starts are usually within seconds.

So GPS Is Better Right?

Keeping an objective mind, I would say there is always right answer whereby one is better than the other. It all depends on your usage, as always. If you are always working navigating the city, aGPS would be more useful because you can even track locations when you are indoors or underground (provided you get cellular covergae). But if you are in relatively open spaces, the GPS might do you good.

Then there is subject of availability. Even if you wanted aGPS, your carrier may not support it on your device’s model. Or if they did, they might charge you for it. GPS is free and within your control while aGPS is more dependent on your carrier than you might like.

My Choice?

If it were up to me to choose, I would go with GPS. I prefer being able to control what I need to use rather than leaving it to my carrier. Because, I might just switch carriers next month and if they do not support my device, it would be troublesome for me. Plus the added bonus that I can use my device in foreign countries without having to turn my phone on (and get a huge roaming bill when I return) is a big plus for me.

What would your choice be?

This post was written because I have received several interesting enquiries about GPS and aGPS and also after I read WMExperts quick tutorial on the debate.  

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