Wireless phones or cell phones are like a two-way radio which has in-built antennas and which are held by hand. Cell phones are a sophisticated form of radio. Unlike CB radio or walkie-talkie in which only one person can speak at a time, Cell phone is a device in which one frequency is used for talking while the other frequency is used for listening.
Cells present in the cell phone provide a very good range as compared to a walkie-talkie, which has a range of one mile, and CB radio, which can transmit frequencies up to five miles. While a CB radio has 40 channels, a Cell phone has 1664 channels.
Radio waves or frequencies are transmitted by the phones to a nearby wireless telephone base station which forwards the call through telephone network to the person you want to call.
Wireless telephone base stations, also known as cellular base stations, cell stations or telephone transmission towers, are fixed antennas which are generally located on towers, rooftops and poles etc. There are two types of antennas which are used in base stations – omni-directional antennas and panel or sector antennas.
While omni-directional antennas look like poles and are usually installed in rural areas, panel or sector antennas are used in urban and sub-urban areas and comprise of rectangular panels. The antennas have groups of three antennas each out of which one is used for transmitting signals to wireless phones while the other two are used for receiving signals.
There are two types of cell phone systems – analog and digital.
Analog Cell Phone Systems modulate the audio directly to a carrier. In the US, three types of analog cell phone system is prevalent – Advanced Mobile Phone Systems (AMPS), Extended AMPS (EAMPS) and Narrowband AMPS (NAMPS).
AMPS is the oldest system which has 666 channels comprising 624 voice channels and 42 control channels. EAMPS is the new standard in the US which has 832 channels consisting of 790 voice channels and 42 control channels. NAMPS is the latest version of analog cell phone system which has 42 control channels and around 2670 voice channels.
While control channels are used to set up calls, voice channels are used for holding conversations.
Digital systems convert audio to numbers like 1s and 0s, which represent voltage levels at particular points. These numbers are then converted to voltage levels. GSM and CDMA are the examples of digital cell phone system.
Global System for Mobile Communications or GSM, as it is popularly known, is a cellular network in which mobile phones search for the cells in the immediate vicinity to connect within the network. GSM phones use SIM cards or Subscriber Identity Module cards which stores information relating to users’ subscription and phone book. These cards enable the user to switch to a different phone. If the user wants to switch to a different carrier, he can do so by disposing off the SIM card while retaining the phone.
GSM phones can be used even if the user has gone abroad by simply buying a SIM card in that country. GSM-enabled cell phones have a better network in rural and far-flung areas.
Code Division Multiple Access or CDMA, as it is popularly known, is a dominant standard in North America and parts of Asia. Most of the CDMA phones, especially those in the US, are linked to one carrier as a result one has to throw the old phone to switch to a different carrier or a new cell phone. CDMA-enabled cell phones are faster when compared to GSM mobiles.