GENERAL INFO

Global Positioning System (GPS) : A Complete Review
By: Tyson J Stevenson
The system of knowing one's exact position on this earth is known as the 'Global Positioning System'. Precise positioning of any location can easily be done with the help of this System. If anyone has a Global Positioning System receiver and if the sky remains clear then no one is going to be lost on this Earth. The receiver is a pocket-sized gadget that makes us inform about our exact position on this earth at any moment. One thing is that this pocket-sized gadget or receiver is very expensive and it also involves a lot of technical ingenuity. The primary function of Global Positioning System is the navigation in three dimensions. The Navigation receivers are used for aircraft, ships, and ground vehicles and sometimes it is also carried in hands by individual.

The working of the System
The GP System provides some special satellite signals which is processed in the receiver. These GPS receivers not only track the exact location but can also compute velocity and time. The positions can even be computed in three dimensional views with the help of four GPS satellite signals. The Space Segment of the Global Positioning System consists of 27 Earth-orbiting GPS satellites. There are 24 operational and 3 extra (in case one fails) GPS satellites. These satellites move round the Earth in 12 hours and send radio signals from space that is being received by the GPS receiver. The control of the Positioning System consists of different tracking stations that are located across the world. These monitoring stations help in tracking signals from those GPS satellites that are continuously orbiting the earth. The Space Vehicles transmit microwave carrier signals. The users of the Global Positioning System have GPS receivers that can convert the satellite signals by which one can estimate the actual position, velocity and time. Four satellites are required to track the three dimensional location and time. The operation of the system is based on a simple mathematical principle called Trilateration. The Trilateration may be of two types i.e. 2-D Trilateration and 3-D Trilateration. In order to make the simple mathematical calculation the GPS receiver should know two things. Firstly the location of the place is to be traced by at least three satellites above the place. Second is the distance between the place and each of those Space Vehicles. Units those have multiple receivers can pick up signals from several GPS satellites at a same time. These radio waves are electromagnetic energy that travels at the speed of light.

Overview
GPS is specially a Satellite Navigation System that helps in tracking the exact location with the help of satellites. The Global Positioning System is mainly funded and controlled by the U.S Department of Defense (DOD). The system was initially designed for the operation of U. S. military. But today, there are also many civil users of GPS across the whole world. The civil users are allowed to use the Standard Positioning Service without any kind of charge or restrictions.

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WHAT Does GSM, Lock & Unlock Mean
By: Victor Epand
The term GSM means - Global System for Mobile Communications. It is the most popular standard for mobile phones in the world. GSM differs significantly from its predecessors in that both signaling and speech channels are Digital call quality, which means that it is considered a second generation (2G) mobile phone system. GSM is an open standard which is currently developed by the 3rd Generation Partnership Project (3GPP). From the point of view of the consumer, the key advantage of GSM systems has been higher digital voice quality and low cost alternatives to making calls such as text messaging. The advantage for network operators has been the ability to deploy equipment from different vendors because the open standard allows easy inter-operability. Like other cellular standards GSM allows network operators to offer roaming services which mean subscribers can use their phones all over the world.

To help you further understand, GSM is simply a standard used by phones to communicate with each other. It is a new standard that has been adopted to all new models of phones and is now so prevailant that it has become the 'norm' in the phone world. Now to answer your other question, with respect to locked and unlocked phones. A phone is locked when it is attached to network. For example if you go to AT&T and purchase a phone from them then that phone is said to be locked unto the AT&T network and as such it cannot work on another network such as SPRINT or NEXTEL. Thus an unlocked phone is a phone that is bought, that is not locked to any network. And as such it can work on any network. The network it will lock unto will depend on the SIM card you put into the phone. For example if you put a AT&T sim in an unlocked phone then it will work on the AT&T network. In the same way if you put a NEXTEL SIM card in an unlocked phone then it will work on the NEXTEL network. However if the phone is locked to a particular network, like say for example AT&T then changing the SIM card in the phone to another SIM card from another network such as NEXTEL will not work. This is because the phone is locked unto to AT&T network and as such will not work on any other network.

Yes, you can use the prepaid SIM card on the phone once the phone is either unlocked or on the same network as the SIM card you are going to put into it. It should work just fine. Unfortunatly is isn't possible to have more than one phone on the same line. It is possible to have more to than one phone on the same account, in fact, some providers will allow many many lines on one account. The reason why your unable to do this is that your phone has a ESN (electronic serial number) that assoicated with that line. What this does is allow your network to send the calls to your phone. If there is more then one ESN per line then it will cause problems receiving calls. For example, I had a phone that i wasnt using anymore when i bought a new one, well my old phone was recieving text messages that my new one was supposed to get, but the new one would get all the calls. To resolve the issue that had to erase the programming on the phone.