Demodulationsreferenzsignale

Demodulation is the process of extracting the original information-bearing signal from a modulated carrier. It is the counterpart to modulation and is used in receivers across radio, television, and data communications to recover either analog or digital data.

In analog systems, demodulation recovers an analog signal from carriers that have been modified in amplitude, frequency, or phase. Common methods include envelope detection for amplitude modulation, frequency discrimination for frequency modulation, and phase-locked loop techniques for phase modulation. In digital systems, demodulation converts a modulated waveform back into a stream of digital symbols or bits, often implemented with coherent or noncoherent techniques.

Coherent demodulation relies on a reference carrier and precise synchronization of frequency and phase to detect symbols, enabling high spectral efficiency with formats such as QPSK and various QAM constellations. Noncoherent demodulation does not require a known carrier phase, and is used for certain modulations like some frequency-shift keying schemes, trading off performance for simpler receiver design. Digital demodulation typically involves filtering, sampling, symbol timing recovery, and decision logic (often followed by error-detecting or error-correcting decoding).

The performance of a demodulator depends on channel conditions, noise, distortion, and synchronization accuracy. Metrics such as bit error rate and symbol error rate quantify its effectiveness. Demodulation is embedded in the front-end of communication receivers and interacts with downconversion, filtering, equalization, and decoding to recover the transmitted information reliably.