Telecommunication Basics

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The purpose of any telecommunications system is to transfer information from the sender to the receiver by a means of a communication channel.The information is carried by a signal, which is certain physical quantity that changes with time.
The signal can be a voltage proportional to the amplitude of the voice,
like in a simple telephone, a sequence of pulses of light in an optical fibre, or a radio-electric wave irradiated by an antenna.
For analog signals, these variations are directly proportional to some physical variable like sound, light, temperature, wind speed, etc. The information can also be transmitted by digital binary signals, that will have only two values, a digital one and a digital zero. Any analog signal can be converted into a digital signal by appropriately sampling and then coding it. The sampling frequency must be at least twice the maximum frequency
present in the signal in order to carry all the information contained therein. Random signals are the ones that are unpredictable and can be described only by statistical means.

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