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Quadrature amplitude modulation (QAM) can be considered a subset of APSK because all QAM schemes modulate both the amplitude and phase of the carrier. Conventionally, QAM constellations are rectangular and APSK constellations are circular, however this is not always the case.
Digital 16-QAM with example symbols Constellation points for 4-QAM, 16-QAM, 32-QAM, and 64-QAM overlapped. As in many digital modulation schemes, the constellation diagram is useful for QAM. In QAM, the constellation points are usually arranged in a square grid with equal vertical and horizontal spacing, although other configurations are ...
The input sinusoidal voltage is usually defined to have zero phase, meaning that it is arbitrarily chosen as a convenient time reference. So the phase difference is attributed to the current function, e.g. sin(2 π ft + φ), whose orthogonal components are sin(2 π ft) cos(φ) and sin(2 π ft + π /2) sin(φ), as we have seen.
A 'signal space diagram' is an ideal constellation diagram showing the correct position of the point representing each symbol. After passing through a communication channel, due to electronic noise or distortion added to the signal, the amplitude and phase received by the demodulator may differ from the correct value for the symbol. When ...
A common form of decision-directed carrier recovery begins with quadrature phase correlators producing in-phase and quadrature signals representing a symbol coordinate in the complex plane. This point should correspond to a location in the modulation constellation diagram .
Amplitude modulation (AM) is a modulation technique used in electronic communication, most commonly for transmitting messages with a radio wave.In amplitude modulation, the amplitude (signal strength) of the wave is varied in proportion to that of the message signal, such as an audio signal.
A multiplexing technique may be further extended into a multiple access method or channel access method, for example, TDM into time-division multiple access (TDMA) and statistical multiplexing into carrier-sense multiple access (CSMA). A multiple-access method makes it possible for several transmitters connected to the same physical medium to ...
The most common example of frequency-division multiplexing is radio and television broadcasting, in which multiple radio signals at different frequencies pass through the air at the same time. Another example is cable television , in which many television channels are carried simultaneously on a single cable.