The Technology of Cell Phones

General characteristics
A cell phone is a low-power (1-2 W) transceiver. It transmits voice and data to the nearest cell bases ranging between 5 to 8 miles (approx. 8 to 13 km). When the cell phone is turned on, it is registered as a unique identifier. If it is solicited, then the device is alerted and the user receives an incoming call.

Cell bases broadcast their presence via low-power transmitters which settles communications between the mobile handsets and the switch. The switch has the function to connect the call to the solicited subscriber (of the same wireless service provider or included networks).

The technology, which assures the connection between the handset and the cell base, depends on the system adopted by the provider. The signal is a stream of digital data that includes digitized audio (excluding 1st generation analog networks).

Networks

There are two types of cell telephone networks:
analog networks (AMPS)
digital networks (D-AMPS, CDMA, GSM, GPRS, EV-DO, UMTS).

Today all providers have switched to digital networks and only a few of them are still running analog networks. They do this for users with older models of phones supporting only analog connections. If you have a modern phone, you can be sure that you are connected to a digital network.

Digital networks are also known as Second Generation technologies. They differ either by technology or by speed.

The most used digital networks are:
CDMA (Code-Division Multiple Access). Is used by more than half of the customers of North-America, and countries such as South Korea.
TDMA (Time Division Multiple Access). It is considered an outdated digital technology and is used by a few providers;
GSM (Global System for Mobile communication). It is the most popular digital network. It is widely used by Europeans, nearly half of North Americans and lots of people from other countries.

These three technologies are not to be compared, because each of them has its pros and cons. Still, some people consider that GSM phones (over 1,5 billion users around the world) are more comfortable to use. The GSM phones are provided with SIM card slots. A SIM card is a small card that contains information about your phone number, address book, and the setup information. The card can be easily removed and then inserted into another cell phone device. It is technically possible to use a SIM card in CDMA phones, but a few cell phone devices and networks support cards.

Frequency

Each network provider has a unique radio frequency band. The lower the frequency is, the better connection is provided. At the same time, the higher the frequency is, the further the cell bases transmits. Thus, providers that assure lower frequency have to install more towers to cover the same territory. High frequencies (1900 MHz) are provided in rural area, which means less towers are installed.

For GSM networks four frequencies available: 850, 900, 1800 and 1900 MHz. Europe uses 900 and 1800 MHz, whereas North America communicates at 850 and 1900 Mhz.

There exist GSM phones that can support two, three or four frequencies. They are called 'double band', 'tri-band' and 'quad-band' respectively. For example, a double band phone from North America will support 850 and 1900MHz. This means you can use it with the networks that provide these frequencies. You can have the same phone supporting 900 and 1800 MHz channels, and you can use it mainly in Europe.

'World' phones also exist! They can be used everywhere, as they have more frequencies.

It should be mentioned that CDMA phones use the same frequencies as GSM. But the GSM phones are only digital. And CDMA and TDMA phones usually support both digital and analog networks.

If you have to travel far away from urban area and digital providers, then a CDMA phone (supporting an analog network on 850 Mhz and digital networks on 850 MHz and 1900 Mhz) will do just great. So your choice of phone (CDMA or GSM provider) depends on what your lifestyle.

The most popular newcomer in the world of technologies is about the 3G (3r Generation). It comprises both EVDO (Evolution Data Optimized) used CDMA providers and UMTS (Universal Mobile Communication System) used by GSM companies. These technologies will allow to deliver up to 15 Mbps. This is even faster than the speed broadband Internet connections provide today. These networks are already used in Europe. Most of the latter smartphones support these technologies.
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