 Signal processing

Signal processing is an area of systems engineering, electrical engineering and applied mathematics that deals with operations on or analysis of signals, in either discrete or continuous time. Signals of interest can include sound, images, timevarying measurement values and sensor data, for example biological data such as electrocardiograms, control system signals, telecommunication transmission signals, and many others. Signals are analog or digital electrical representations of timevarying or spatialvarying physical quantities. In the context of signal processing, arbitrary binary data streams and onoff signalling are not considered as signals, but only analog and digital signals that are representations of analog physical quantities.
Contents
Typical operations and applications
Processing of signals includes the following operations and algorithms with application examples:^{[1]}
 Filtering (for example in tone controls and equalizers)
 Smoothing, deblurring (for example in image enhancement)
 Adaptive filtering (for example for echocancellation in a conference telephone, or denoising for aircraft identification by radar)
 Spectrum analysis (for example in magnetic resonance imaging, tomographic reconstruction and OFDM modulation)
 Digitization, reconstruction and compression (for example, image compression, sound coding and other source coding)
 Storage (in digital delay lines and reverb)
 Modulation (in modems and radio receivers and transmitters)
 Wavetable synthesis (in modems and music synthesizers)
 Feature extraction (for example speechtotext conversion and optical character recognition)
 Pattern recognition and correlation analysis (in spread spectrum receivers and computer vision)
 Prediction
 A variety of other operations
In communication systems, signal processing may occur at OSI layer 1, the Physical Layer (modulation, equalization, multiplexing, etc.) in the seven layer OSI model, as well as at OSI layer 6, the Presentation Layer (source coding, including analogtodigital conversion and data compression).
History
According to Alan V. Oppenheim and Ronald W. Schafer, the principles of signal processing can be found in the classical numerical analysis techniques of the 17th century. They further state that the "digitalization" or digital refinement of these techniques can be found in the digital control systems of the 1940s and 1950s.^{[2]}
Mathematical topics embraced by signal processing
 Linear signals and systems, and transform theory
 System identification and classification
 Calculus
 Differential equations
 Vector spaces and Linear algebra
 Functional analysis
 Probability and stochastic processes
 Detection theory
 Estimation theory
 Optimization
 Programming
 Numerical methods
 Iterative methods
Categories of signal processing
Analog signal processing
Main article: analog signal processingAnalog signal processing is for signals that have not been digitized, as in classical radio, telephone, radar, and television systems. This involves linear electronic circuits such as passive filters, active filters, additive mixers, integrators and delay lines. It also involves nonlinear circuits such as compandors, multiplicators (frequency mixers and voltagecontrolled amplifiers), voltagecontrolled filters, voltagecontrolled oscillators and phaselocked loops.
Discrete time signal processing
Discrete time signal processing is for sampled signals that are considered as defined only at discrete points in time, and as such are quantized in time, but not in magnitude.
Analog discretetime signal processing is a technology based on electronic devices such as sample and hold circuits, analog timedivision multiplexers, analog delay lines and analog feedback shift registers. This technology was a predecessor of digital signal processing (see below), and is still used in advanced processing of gigahertz signals.
The concept of discretetime signal processing also refers to a theoretical discipline that establishes a mathematical basis for digital signal processing, without taking quantization error into consideration.
Digital signal processing
Main article: digital signal processingDigital signal processing is the processing of digitised discrete time sampled signals. Processing is done by generalpurpose computers or by digital circuits such as ASICs, fieldprogrammable gate arrays or specialized digital signal processors (DSP chips). Typical arithmetical operations include fixedpoint and floatingpoint, realvalued and complexvalued, multiplication and addition. Other typical operations supported by the hardware are circular buffers and lookup tables. Examples of algorithms are the Fast Fourier transform (FFT), finite impulse response (FIR) filter, Infinite impulse response (IIR) filter, and adaptive filters such as the Wiener and Kalman filters.
Fields of signal processing
 Statistical signal processing — analyzing and extracting information from signals and noise based on their stochastic properties
 Audio signal processing — for electrical signals representing sound, such as speech or music
 Speech signal processing — for processing and interpreting spoken words
 Image processing — in digital cameras, computers, and various imaging systems
 Video processing — for interpreting moving pictures
 Array processing — for processing signals from arrays of sensors
 Timefrequency signal processing — for processing nonstationary signals^{[3]}
 Filtering — used in many fields to process signals
 Seismic signal processing
 Data mining.
See also
Notes and references
 ^ Mathematical Methods and Algorithms for Signal Processing, Todd K. Moon, Wynn C. Stirling, Prentice Hall, 2000, ISBN 0201361868, page 4.
 ^ Oppenheim, Alan V.; Schafer, Ronald W. (1975). Digital Signal Processing. Prentice Hall. p. 5. ISBN 0132146355.
 ^ Boashash, B. (ed.), (2003) TimeFrequency Signal Analysis and Processing: A Comprehensive Reference, Elsevier Science, Oxford, 2003; ISBN 0080443354
External links
 Signal Processing for Communications — free online textbook by Paolo Prandoni and Martin Vetterli (2008)
 Scientists and Engineers Guide to Digital Signal Processing — free online textbook by Stephen Smith
 Signal Processing and Recognition Group
Categories: Media technology
 Signal processing
 Telecommunication theory
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