Modulationer

Modulation is the process of altering a carrier signal to encode information for transmission over a communication channel. By changing properties such as amplitude, frequency, or phase, modulation enables efficient use of bandwidth, long-distance transmission, and multiplexing of signals. Modulation methods are typically categorized as analog or digital, and as linear or nonlinear with respect to the carrier.

Analog modulation includes amplitude modulation (AM), frequency modulation (FM), and phase modulation (PM). AM varies the carrier amplitude in proportion to the message; FM varies the carrier frequency; PM varies the phase. These methods are used in radio broadcasting and navigation, with demodulation performed by envelope detectors for AM or discriminators for FM/PM.

Digital modulation maps digital data to symbols on a carrier. Common schemes include amplitude-shift keying (ASK), frequency-shift keying (FSK), phase-shift keying (PSK), and quadrature amplitude modulation (QAM), with QAM combining amplitude and phase for higher data rates. Modern systems use complex schemes and multi-carrier approaches like OFDM to improve spectral efficiency and resilience.

Practical considerations and demodulation: The choice affects bandwidth, power efficiency, and noise robustness. Demodulation can be coherent or non-coherent, depending on the scheme. In practice, receivers are designed to match the modulation for reliable data recovery, and channel conditions influence the optimal choice.

History and impact: Modulation theory emerged in the early 20th century with developments in radio communication and later digital communications. It underpins broadcasting, mobile networks, satellite links, and data networks worldwide.