How Is One Mobile Connected to Another?

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Each year millions of people will take out their mobile phone, dial a number and get connected to another person without giving a thought to the process behind the connection. While mobile communication has had numerous technological advances since its inception, it works on the same basic principles as the earliest two-way radios.

History

  • Mobile communication began as scientists and engineers improved upon the one-way radios that were prevalent in the early 1900s. Small improvements in mobile technology built upon each other until the 1980s, when cellular tower designs allowed for complete service coverage across a region.

Radio Communications

  • Your cell phone, put in simple terms, is a small computer connected to a radio antenna. The radio in your phone connects with the cellular network using electromagnetic waves on a certain frequency. The radio, controlled by computers in both your cell phone and the tower, uses slight frequency modulations to transmit information. In early radios this frequency modulation would result in speaker movement, which we hear as sound. With the advent of computer technology, these frequency modulations along with digital modulation schemes are used to transmit information as binary code which the computer on the receiving end can interpret.

Types of Connections

  • As of 2010, two main types of radio connections are being used: TDMA and CDMA, named after the method that they use to allow multiple people to use the same frequency. TDMA, or Time Division Multiple Access, breaks down the frequency into a number of time slots. Each connection between a cell phone and a tower is assigned a time slot, so that multiple people can use the same frequency to communicate. CDMA, or Code Division Multiple Access, makes changes to the frequency of the transmission according to a defined pattern, or code. Both the phone and the tower use this unique code to reassemble the message.

Cellular Coverage

  • Your cell phone can only communicate with towers within a few miles due to size and power constraints. In order to ensure complete coverage, mobile towers need to be installed at regular intervals, with each tower handling communications over a geographical area called a cell. When a phone signal starts to diminish because the user is moving out of range of the tower, the tower notifies the central network and the call is routed to a cell with a stronger signal. The phone is briefly connected to two towers simultaneously so that switching of the call between cell towers happens without the user even knowing anything has changed.

Central Networks

  • All the cell towers in a geographical region, usually the size of a large city, are connected to the same central office, called a Mobile Telephone Switching Office. The MTSO is in charge of all the connections for a service provider over a geographical area. When you make a call with your cell phone, the cell tower notifies the MTSO, who then must correctly route the call. The call could get routed back to the same tower, to another tower in the region, to another MTSO operated by the same service provider or to the public telephone system for a connection to another provider.

References

  • Photo Credit cell phone tower image by Aaron Kohr from Fotolia.com
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