Baaq (Signal)

A signal is a measurable change that carries information and can be detected at one location and transmitted to another. Signals can be electrical voltage, radio waves, light, sound, or digital data. What matters is not the physical form of the signal, but rather that its variation is related to the information intended to be conveyed.

A signal is defined as a function dependent on time or location. When a signal is plotted against time, its variation in value over a period is observed. Signal processing is the discipline concerned with how signals are measured, filtered, stored, and how information within them is extracted.

Types of signals

The most common classification is between analog and digital signals. An analog signal changes its value continuously; for example, the voltage from a microphone. A digital signal takes on discrete numerical values, typically two levels (0 and 1). An analog signal can be converted to digital form by sampling at fixed time intervals and then quantizing the values into numbers.

Signals are also distinguished as either non-periodic or periodic. Periodic signals, such as sine waves, are defined by wavelength, frequency, and phase. Fourier analysis shows that any well-behaved signal can be decomposed into sine waves of different frequencies.

Signal noise and quality

Any transmitted signal is accompanied by noise, unwanted variation arising from equipment imperfections, electrical interference, or transmission conditions. Signal quality is measured by the signal-to-noise ratio. When this ratio is low, extracting information becomes difficult. Filtering techniques and error correction codes are used to reduce noise.

Applications

Signals are fundamental to communications: telephones, radio, television, internet networks, and satellite positioning systems (GPS) all operate by transmitting signals. In medicine, signals are used to measure bodily functions, such as heart activity (ECG) and brain activity (EEG). In control engineering, signals fed back from a device are used to adjust system performance.