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Digital modulation methods can be considered as digital-to-analog conversion and the corresponding demodulation or detection as analog-to-digital conversion. The changes in the carrier signal are chosen from a finite number of M alternative symbols (the modulation alphabet). Schematic of 4 baud, 8 bit/s data link containing arbitrarily chosen ...
During each symbol, the phase either remains the same, encoding a 0, or jumps by 180°, encoding a 1. Again, only one bit of data (i.e., a 0 or 1) is transmitted by each symbol. This is an example of data being encoded in the transitions between symbols (the change in phase), rather than the symbols themselves (the actual phase).
Afterwards, the two signals are superimposed, and the resulting signal is the QPSK signal. Note the use of polar non-return-to-zero encoding. These encoders can be placed before for binary data source, but have been placed after to illustrate the conceptual difference between digital and analog signals involved with digital modulation.
Frequency modulation (FM) is the encoding of information in a carrier wave by varying the instantaneous frequency of the wave. The technology is used in telecommunications , radio broadcasting , signal processing , and computing .
An example of coding a binary signal using rectangular pulse-amplitude modulation with polar non-return-to-zero code An example of bipolar encoding, or AMI. Encoding of 11011000100 in Manchester encoding An example of differential Manchester encoding An example of biphase mark code An example of MLT-3 encoding
The binary signal is encoded using rectangular pulse-amplitude modulation with polar NRZ(L), or polar non-return-to-zero-level code. In telecommunications, a non-return-to-zero (NRZ) line code is a binary code in which ones are represented by one significant condition, usually a positive voltage, while zeros are represented by some other significant condition, usually a negative voltage, with ...
In MSK, the difference between the higher and lower frequency is identical to half the bit rate. Consequently, the waveforms that represent a 0 and a 1 bit differ by exactly half a carrier period. The maximum frequency deviation is δ = 0.25 f m, where f m is the maximum modulating frequency. As a result, the modulation index m is 0.5.
For audio, this type of encoding reduces the number of bits required per sample by about 25% compared to PCM. Adaptive differential pulse-code modulation (ADPCM) is a variant of DPCM that varies the size of the quantization step, to allow further reduction of the required bandwidth for a given signal-to-noise ratio.