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The 3 basic techniques of digital manipulation.
ASK - Amplitude Shift keying stands for a modulation type in which the Amplitude of a carrier signal shifts abruptly between two states. Each carrier state represents one of the two modulating signal states. This system is easily improved in terms of spectral efficiency, when multiple modulation levels are chosen. Downside is the noise susceptibility of amplitude modulations.
PSK - Phase Shift keying is a modulation technique in which the angular momentum of a carrier signal is abruptly shifted by 180dgs in accordance to a level change in input signal. This method allows for efficient transmission of several bits per second if more than two phase states are chosen through which the signal can cycle through. Along with ASK, the two techniques can be combined in a hybrid modulation system with both ASK and PSK, extending the bits per hz ratio even further. Such QAM systems are very often used where spectral efficiency and high bitrate ratio is required. Downside is, there's great requirements for noise in such systems. Even though these systems are widely used in wireless broadcasts, they are most appropriate in environments where the noise level can be monitored and controlled (cable networks).
FSK stands for Frequency Shift Keying in which the momentary frequency of the carrier signal is shifted between two levels. These systems are harder to design, because the designer must take into account mobile receivers in which the doppler shift effect may become problematic. Usually these circuits are easier to build than their analog equivalents, because they have only two momentary states in contrast to the infinite states an analog signal can take, and don't require perfect linearity of the transmitters, but are harder to design in certain environments, where a lousy analog signal will still be intelligible, whereas a lousy digital signal may fall beneath the minimum threshold level of the receiver and become totally unintelligible. This abrupt ,,cease of reception'' slope is what makes digital wireless networks harder to design.
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