Demodulations

Demodulation is the process of extracting the original information-bearing signal from a modulated carrier. In communications, demodulators are used at receivers to recover voice, video, data, or control signals that have been encoded onto a carrier by modulation. Demodulation spans analog and digital domains and applies to radio, television, and data links.

Analog demodulation includes techniques such as envelope detection for amplitude-modulated AM signals, which recovers the modulating waveform from the carrier via a diode detector and an RC filter. Suppressed-carrier schemes (double-sideband suppressed carrier, DSB-SC) require synchronous or product detectors. Frequency-modulated FM demodulation uses discriminators, ratio detectors, or phase-locked loop based receivers.

In digital communications, demodulation refers to converting a received signal into a stream of symbols. Coherent demodulation assumes a known carrier reference and performs matched filtering and decision making; non-coherent methods do not require carrier phase tracking. Common schemes include BPSK, QPSK, QAM, and FSK, often followed by error correction to improve reliability.

Demodulation performance is affected by noise, distortion, and channel impairments. Synchronization for carrier and timing is essential; techniques such as differential demodulation, pilot symbols, and adaptive equalization mitigate phase ambiguity and distortion. Soft-decision demodulation can improve error rates compared with hard decision.

Demodulation underpins modern communication systems, enabling reception of radio, television, mobile data, and fiber-optic links. Advances include digital signal processing based demodulators, multi-antenna reception, and software-defined radio architectures.