A communication system is a set of components and protocols that transmit information from a source to a destination. It typically involves a transmitter, a transmission medium, and a receiver.
Analog communication transmits information using continuous signals that vary in amplitude, frequency, or phase. Digital communication transmits information using discrete signals, usually represented as binary data (0s and 1s).
Modulation is the process of varying a carrier signal in order to transmit data. It is needed to efficiently transmit signals over long distances, reduce the size of antennas, and enable multiplexing to transmit multiple signals over the same channel.
There are several types of modulation, including:
FDM is a technique where multiple signals are transmitted simultaneously over a single communication channel by dividing the available bandwidth into non-overlapping frequency bands, each carrying a separate signal.
TDM is a technique where multiple signals are transmitted over a single communication channel by dividing the transmission time into time slots, with each slot allocated to a different signal.
The Nyquist Theorem states that to accurately sample a continuous signal without aliasing, the sampling rate must be at least twice the highest frequency present in the signal. This is crucial for designing efficient sampling systems in digital communication.
Baseband transmission involves sending a signal in its original frequency range over a channel without modulation, typically over short distances. Broadband transmission involves modulating the signal to higher frequencies for transmission over longer distances or shared media.
QAM is a modulation scheme that conveys data by changing the amplitude of two carrier waves, which are out of phase by 90 degrees (quadrature). It combines both amplitude and phase modulation to transmit data efficiently.
OFDM is a digital modulation technique that divides the available spectrum into many orthogonal sub-carriers, each carrying a portion of the user data. It is used to reduce interference and multipath fading, common in wireless communications.