A discipline that deals generally with the extraction of information from acoustic signals in the presence of noise and uncertainty. Acoustic signal processing has expanded from the improvement of music and speech sounds and a tool to search for oil and submarines to include medical instrumentation; techniques for efficient transmission, storage, and presentation of music and speech; and machine speech recognition. Undersea processing has expanded to studying underwater weather and long-term global ocean temperature changes, mammal tracking at long ranges, and monitoring of hot vents. These techniques stem from the rapid advances in computer science, especially the development of large, inexpensive memories and ever-increasing processing speeds.

Signal processing is a discipline that deals with the extraction of information from signals. The devices that perform this task can be physical hardware devices, specialized software codes, or combinations of both. In recent years the complexity of these devices and the scope of their applications have increased dramatically with the rapidly falling costs of hardware and software and the advancement of sensor technologies. This trend has made it possible to pursue sophisticated signal-processing designs at relatively low cost. Some notable applications, in areas ranging from biomedical engineering to wireless communications, include the suppression of interference arising from noisy measurement sensors, the elimination of distortions introduced when signals travel through transmission channels, and the recovery of signals embedded in a multitude of echoes created by multipath effects in mobile communications.

Radar equipment carried by commercial and military aircraft. These aircraft use airborne radar systems to assist in weather assessment and navigation. Military systems also provide other specialized capabilities such as targeting of hostile aircraft for air-to-air combat, detection and tracking of moving ground targets, targeting of ground targets for bombing missions, and very accurate terrain measurements for assisting in low-altitude flights. Airborne radars are also used to map and monitor the Earth's surface for environmental and topological study.

The process or result of the process whereby the amplitude of a carrier wave is changed in accordance with a modulating wave. This broad definition includes applications using sinusoidal carriers, pulse carriers, or any other form of carrier, the amplitude factor of which changes in accordance with the modulating wave in any unique manner. See also: Modulation

A device for moving the frequency of an information signal, which is generally at baseband (such as an audio or instrumentation signal), to a higher frequency, by varying the amplitude of a mediating (carrier) signal. The motivation to modulate may be to shift the signal of interest from a frequency band (for example, the baseband, corresponding to zero frequency or dc) where electrical disturbances exist to another frequency band where the information signal will be subject to less electrical interference; to isolate the signal from shifts in the dc value, due to bias shifts with temperature or time of the characteristics of amplifiers, or other electronic circuits; or to prepare the information signal for transmission.

The channel bandwidths needed to transmit various types of signals, using various processing schemes. Propagation conditions for communication systems that transmit signals through the atmosphere or through free space are strongly dependent on the transmission frequency. Government regulations specify the modulation type, the bandwidth, and the type of information that can be transmitted over designated frequency bands. In the United States, the Federal Communications Commission (FCC) regulates radio, telephone, television, and satellite transmission systems. In North America, standards are developed by the Institute of Electrical and Electronics Engineers (IEEE), by Committee TI–Telecommunications (accredited by the American National Standards Institute, ANSI), and by the Telecommunications Industry Association (TIA). Internationally, frequency assignment and technical standards are developed by the International Telecommunications Union–Telecommunications Standardization Sector (ITU-T) and the International Telecommunications Union–Radiocommunication Sector (ITU-R), functioning under the auspices of the United Nations International Telecommunications Union (ITU). See also: Radio spectrum allocation

Technology that employs a distinctive, measurable biological or behavioral characteristic that can reliably distinguish one individual from another (biometric) for authentication, identification, and verification of individuals. Biometric authentication is the process of confirming the identity of an individual by comparing the individual's biometric sample against (1) one or more previously collected reference samples (biometric identification) or (2) a specific reference sample based on the individual's claimed identity (biometric verification). Biometric identification is a one-to-many process, and biometric verification is a one-to-one process. Biometric technologies commonly used for authentication and identification in access control systems include fingerprints, iris, voice, and face recognition (see figure), with applications broadly ranging from healthcare to government benefit administration to aviation security. See also: Aviation security; Biometrics; Fingerprint; Fingerprint identification

A periodic waveform upon which an information-bearing signal is impressed. This process is known as modulation and comprises a variety of forms such as amplitude, phase, and frequency modulation. The most common type of carrier is the sinusoidal carrier (illus.a), but in reality, any periodic waveform followed by a band-pass filter can serve as a carrier.

Cameras in mobile phones or smartphones that can capture images and videos. Over the decades since their introduction in the 1970s, cellphones—also known as mobile phones—have experienced continuous and often dramatic improvements. Much of the earlier progress was accomplished by optimizing telecommunications technology, which has included periodically advancing transmission and network protocols. These improvements have been grouped into "generations" of technology, for instance with the third generation, 3G, established in 2001, and 4G, established in approximately 2009, and then into 5G since about 2019. Each generation represents improvements in quality, reduction of power, and great increase in the number of calls-per-region capacity. Battery life has likewise advanced, with improvements in lower power consumption afforded by high-density computer chips. The devices' electronic displays have accordingly improved as well, for instance with the introduction of high-resolution, so-called retina screens in the early 2010s, where the human eye can no longer distinguish individual pixels. In association with these widespread advances, cellphone camera technologies have advanced tremendously as well and been of keen interest to consumers, helping to define phones and differentiate brands while also setting price ranges. See also: 5G communications; Battery; Electronic display; Mobile communications; Vision

An electrical transmission line comprising an inner, central conductor surrounded by a tubular outer conductor. The two conductors are separated by an electrically insulating medium which supports the inner conductor and keeps it concentric with the outer conductor. One version of coaxial cable has periodically spaced polyethylene disks supporting the inner conductor (Fig. 1). This coaxial is a building block of multicoaxial cables used in L-carrier systems. See also: Transmission lines