differential modulation - ορισμός. Τι είναι το differential modulation
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Τι (ποιος) είναι differential modulation - ορισμός

SIGNAL ENCODER
Differential Pulse Code Modulation; Differential PCM; Differential pulse code modulation; Dpcm; DPCM

Differential pulse-code modulation         
Differential pulse-code modulation (DPCM) is a signal encoder that uses the baseline of pulse-code modulation (PCM) but adds some functionalities based on the prediction of the samples of the signal. The input can be an analog signal or a digital signal.
Adaptive differential pulse-code modulation         
TECHNIQUE USED TO ENCODE VOICES IN TELEPHONY
ADPCM; IMA ADPCM; Adaptive Differential Pulse Code Modulation; Adaptive quantization; Adaptive Differential Pulse-Code Modulation; SB-ADPCM; Sub-band ADPCM; Adaptive DPCM; Sub-band adaptive differential pulse-code modulation; Adaptive differential PCM
Adaptive differential pulse-code modulation (ADPCM) is a variant of differential pulse-code modulation (DPCM) that varies the size of the quantization step, to allow further reduction of the required data bandwidth for a given signal-to-noise ratio.
Modulation         
  • A low-frequency message signal (top) may be carried by an AM or FM radio wave.
  • Categorization for signal modulation based on data and carrier types
  • [[Waterfall plot]] of a 146.52 MHz radio carrier, with amplitude modulation by a 1,000 Hz sinusoid. Two strong sidebands at + and - 1 kHz from the carrier frequency are shown.
  •  A carrier, frequency modulated by a 1,000 Hz sinusoid. The [[modulation index]] has been adjusted to around 2.4, so the carrier frequency has small amplitude. Several strong sidebands are apparent; in principle an infinite number are produced in FM but the higher-order sidebands are of negligible magnitude.
PROCESS OF ENCODING INFORMATION BY VARYING PROPERTIES OF A PERIODIC CARRIER WAVEFORM
Modulator; Modulated; Mode of transmission; Pulse modulation; Shift keying; Digital modulation; Pulse Modulation; Modulation (communications); Demod; Periodic current reversal; Pulse modulator; Multi Carrier Modulation; Analog modulation; Modulating signal; Modulation memory; Analog modulation method; Digital modulation method; Digital Modem; Modulated wave; Pulse modulation methods; Pulse time modulation; Automatic digital modulation recognition; Digital carrier modulation; Analog carrier modulation
In electronics and telecommunications, modulation is the process of varying one or more properties of a periodic waveform, called the carrier signal, with a separate signal called the modulation signal that typically contains information to be transmitted. For example, the modulation signal might be an audio signal representing sound from a microphone, a video signal representing moving images from a video camera, or a digital signal representing a sequence of binary digits, a bitstream from a computer.

Βικιπαίδεια

Differential pulse-code modulation

Differential pulse-code modulation (DPCM) is a signal encoder that uses the baseline of pulse-code modulation (PCM) but adds some functionalities based on the prediction of the samples of the signal. The input can be an analog signal or a digital signal.

If the input is a continuous-time analog signal, it needs to be sampled first so that a discrete-time signal is the input to the DPCM encoder.

  • Option 1: take the values of two consecutive samples; if they are analog samples, quantize them; calculate the difference between the first one and the next; the output is the difference.
  • Option 2: instead of taking a difference relative to a previous input sample, take the difference relative to the output of a local model of the decoder process; in this option, the difference can be quantized, which allows a good way to incorporate a controlled loss in the encoding.

Applying one of these two processes, short-term redundancy (positive correlation of nearby values) of the signal is eliminated; compression ratios on the order of 2 to 4 can be achieved if differences are subsequently entropy coded because the entropy of the difference signal is much smaller than that of the original discrete signal treated as independent samples.

DPCM was invented by C. Chapin Cutler at Bell Labs in 1950; his patent includes both methods.