Wireless Phones

Transmission – Mobile phones have incorporated in them low power transmitters. Many cells have two signal power levels: 0.6 W and 3 W (to make a comparison, mention that most radio stations transmit at 4 w). Transmission station send it with low power. Low power transmitters have two advantages:
- The transmissions of stations and transmission of a cell phone does not get very far outside that cell. Therefore, in the diagram above, both can reuse the same frequency 56. Same frequencies can be reused many times across the city.

- Energy consumption of cellular normally function under the battery, its relatively small. Low power means small batteries, making it possible the existence of mobile phones so they can be held in the hand. Communication via mobile phones require a large number of broadcast stations in a given city, regardless of its size. In a typical large city they can have hundreds of towers.

But because so many people use mobile phones, costs remain low per user. All operators in each city also runs one central office called the Mobile Telephone Office (BFTM). This office handles all phone connections in normal land-based, telephone system and controls are all base stations in the region.

Mobile codes – All mobile special codes associated with them. The codes used to identify the phone, the phone owner and operator. Suppose you have on a cell phone, power it and someone tries to call. That call and the following occurs:
- When the phone put into operation, it expects to receive an SID (system identification code – A unique 5-digit) of the control channel. The control channel is a special frequency used by mobile phone and base station transmission to determine certain aspects such as system calls and change channels. If the phone cannot find any control channels, the phone realizes it is out of range and displays the message “no signal”.

- When receiving SID, the phone compares it to the SID programmed into the phone. If the two SID’s are identical, cell phone knows that it is communicating with is part of its internal system.
- Along with the SID, the phone also submits an application for registration and register your location

- BFTM phone in a database – in this way, BFTM knows where your cell is and will find it.
- BFTM site receives the call and tries to find you. The database is consulted to see which cell you are.
- BFTM chooses your frequency pair to, that your phone will use it in that cell to take the call.
- BFTM site communicates with your phone over the control channel  to tell it which frequencies to use, and once your phone and the tower will switch on those frequencies, the call is connected. Call is done through a radio that works in two ways.