Cellular Phones
Cellular System
A cell phone is a type of two-way radio which works in a cellular network. A cellular network is a radio network made up of a number of radio cells (or just cells) each served by a fixed transmitter, known as a cell site or base station. These cells are used to cover different areas in order to provide radio coverage over a wider area than the area of one cell.
A mobile phone sends and receives information (voice messages, fax, computer data, etc) by radio communication. Radio frequency signals are transmitted from the phone to the nearest base station and incoming signals (carrying the speech from the person to whom the phone user is listening) are sent from the base station to the phone at a slightly different frequency. Base stations link mobile phones to the rest of the mobile and fixed phone network.
Once the signal reaches a base station it can be transmitted to the main telephone network, either by telephone cables or by higher frequency radio links between an antenna (e.g. dish) at the base station and another at a terminal connected to the main telephone network.
Each base station provides radio coverage to a geographical area known as a cell. Base stations are connected to one another by central switching centers, which track calls and transfer them as the caller moves from one cell to the next.
Cell Phones, Some Facts
On a "complexity per cubic inch" scale, cell phones are some of the most intricate devices people use on a daily basis. Modern digital cell phones can process millions of calculations per second in order to compress and decompress the voice stream.
A modern cell phone provides 2-way communications using one of several cellular standards (GSM, CDMA, TDMA, AMPs, etc.). It often integrates one of more of the following functions:
- vibrating ringer
- polyphonic ringer
- touch-screen
- still and/or video camera
- broadcast radio receiver (FM)
- MP3 player
- PC connection
- PDA function
- Web browsing
- Navigation Maps
- Bluetooth radio
- WiFi connectivity
A cross continent traveler should look for phones that offer multiple bands, multiple modes or both so that phones works whatever technology and band is in use.
Multiple band - A phone that has multiple-band capability can switch frequencies. For example, a dual-band TDMA phone could use TDMA services in either an 800-MHz or a 1900-MHz system. A quad-band GSM phone could use GSM service in the 850-MHz, 900-MHz, 1800-MHz or 1900-MHz band.
Multiple mode - In cell phones, "mode" refers to the type of transmission technology used. So, a phone that supported AMPS and TDMA could switch back and forth as needed. Similarly a cell phone that supports CDMA and GSM could switch back and forth as needed.
Multiple band/Multiple modes - The best of both worlds allows you to switch between frequency bands and transmission modes as needed. Some mobile phones come with dual SIM option wherein using single phone one can make or receive calls fro two different type of systems.
