Introduction to some existing wireless systems:
For wireless system we consider many factors as its needs such as call duration, traffic in adjacent cell, call rate, atmosphere condition and the terrain. Various characteristics are important to get an idea about how wireless system will work in the real-world for the existing cellular system and how it support the mobile communication. In order to emphasis the communication between the sender and the receiver it should follow some set of rules called communication protocols. For facilitating easy transfer of information there are some steps for open system interconnection (OSI) and international organization for standardization (ISO).
Introduction of advanced mobile phone system (AMPS):
AMPS is the first cellular system used in United States. It uses FM modulation technique for transmitting speech signal, one of the important property is control information was transmitted in digital form using FSK. Which is created by AT&T Bell Labs with the key idea of splitting the entire service area into logical division is called cell. And the divided cell is allocated with specific band from the frequency spectrum.
While AMPS uses the cell radius upto 1 to 16 miles, depending on different factors such as traffic density and density of users. Smaller cells have less thermal noise and more interference and larger cells have more thermal noise and less interference. One of the most important consideration of AMPS is it allows both cell sectoring and splitting.
Some characteristics of AMPS:
The frequency band used in AMPS between 824 MHz to 849 MHz for transmission from reverse link and the frequency band used in the forward link is 869 MHz to 894 MHz. Manchester frequency modulation is used for transmitting data at the rate of the 10kbps, while the control parameters remains the same as in voice transfer.
For transmitting control information and data separate channels are used some control messages are exchanged between the mobile station and the base station has compared with data or voice messages, a smaller number of control channels are employed than voice antennas.
In AMPS the frequency allocation is done by splitting the entire frequency spectrum into two bands B and B and B and A.