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In cryptography, pseudorandom noise is a signal similar to noise which satisfies one or more of the standard tests for statistical randomness. Although it seems to lack any definite pattern, pseudorandom noise consists of a deterministic sequence of pulses that will repeat itself after its period.
In telecommunication and radio communication, spread-spectrum techniques are methods by which a signal generated with a particular bandwidth is deliberately spread in the frequency domain, resulting in a signal with a wider bandwidth. These techniques are used for a variety of reasons, including the establishment of secure communications, increasing resistance to natural interference, noise, and jamming, to prevent detection, to limit power flux density, and to enable multiple-access communications.
A time-domain reflectometer (TDR) is an electronic instrument used to determine the characteristics of electrical lines by observing reflected waveforms.
Radio frequency (RF) is the oscillation rate of an alternating electric current or voltage or of a magnetic, electric or electromagnetic field or mechanical system in the frequency range from around 20 kHz to around 300 GHz. This is roughly between the upper limit of audio frequencies and the lower limit of infrared frequencies; these are the frequencies at which energy from an oscillating current can radiate off a conductor into space as radio waves. Different sources specify different upper and lower bounds for the frequency range.
A submarine communications cable is a cable laid on the sea bed between land-based stations to carry telecommunication signals across stretches of ocean and sea. The first submarine communications cables laid beginning in the 1850s carried telegraphy traffic, establishing the first instant telecommunications links between continents, such as the first transatlantic telegraph cable which became operational on 16 August 1858. Subsequent generations of cables carried telephone traffic, then data communications traffic. Modern cables use optical fibre technology to carry digital data, which includes telephone, Internet and private data traffic.
High frequency (HF) is the ITU designation for the range of radio frequency electromagnetic waves between 3 and 30 megahertz (MHz). It is also known as the decameter band or decameter wave as its wavelengths range from one to ten decameters. Frequencies immediately below HF are denoted medium frequency (MF), while the next band of higher frequencies is known as the very high frequency (VHF) band. The HF band is a major part of the shortwave band of frequencies, so communication at these frequencies is often called shortwave radio. Because radio waves in this band can be reflected back to Earth by the ionosphere layer in the atmosphere – a method known as "skip" or "skywave" propagation – these frequencies are suitable for long-distance communication across intercontinental distances and for mountainous terrains which prevent line-of-sight communications. The band is used by international shortwave broadcasting stations (3.95–25.82 MHz), aviation communication, government time stations, weather stations, amateur radio and citizens band services, among other uses.
Power-line communication carries data on a conductor that is also used simultaneously for AC electric power transmission or electric power distribution to consumers.
In electrical engineering, partial discharge (PD) is a localized dielectric breakdown (DB) of a small portion of a solid or fluid electrical insulation (EI) system under high voltage (HV) stress. While a corona discharge (CD) is usually revealed by a relatively steady glow or brush discharge (BD) in air, partial discharges within solid insulation system are not visible.
In an electric power system, a fault or fault current is any abnormal electric current. For example, a short circuit is a fault in which a live wire touches a neutral or ground wire. An open-circuit fault occurs if a circuit is interrupted by a failure of a current-carrying wire or a blown fuse or circuit breaker. In three-phase systems, a fault may involve one or more phases and ground, or may occur only between phases. In a "ground fault" or "earth fault", current flows into the earth. The prospective short-circuit current of a predictable fault can be calculated for most situations. In power systems, protective devices can detect fault conditions and operate circuit breakers and other devices to limit the loss of service due to a failure.
GNSS reflectometry involves making measurements from the reflections from the Earth of navigation signals from Global Navigation Satellite Systems such as GPS. The idea of using reflected GNSS signal for earth observation became more and more popular in the mid-1990s at NASA Langley research centre and is also known as GPS reflectometry. Research applications of GNSS-R are found in
An intermittent fault, often called simply an "intermittent", is a malfunction of a device or system that occurs at intervals, usually irregular, in a device or system that functions normally at other times. Intermittent faults are common to all branches of technology, including computer software. An intermittent fault is caused by several contributing factors, some of which may be effectively random, which occur simultaneously. The more complex the system or mechanism involved, the greater the likelihood of an intermittent fault.
In the automotive industry, brake-by-wire technology is the ability to control brakes through electrical means. It can be designed to supplement ordinary service brakes or it can be a standalone brake system.
Underwater acoustic communication is a technique of sending and receiving messages below water. There are several ways of employing such communication but the most common is by using hydrophones. Underwater communication is difficult due to factors such as multi-path propagation, time variations of the channel, small available bandwidth and strong signal attenuation, especially over long ranges. Compared to terrestrial communication, underwater communication has low data rates because it uses acoustic waves instead of electromagnetic waves.
Fault detection, isolation, and recovery (FDIR) is a subfield of control engineering which concerns itself with monitoring a system, identifying when a fault has occurred, and pinpointing the type of fault and its location. Two approaches can be distinguished: A direct pattern recognition of sensor readings that indicate a fault and an analysis of the discrepancy between the sensor readings and expected values, derived from some model. In the latter case, it is typical that a fault is said to be detected if the discrepancy or residual goes above a certain threshold. It is then the task of fault isolation to categorize the type of fault and its location in the machinery. Fault detection and isolation (FDI) techniques can be broadly classified into two categories. These include model-based FDI and signal processing based FDI.
Noise-domain reflectometry is a type of reflectometry where the reflectometer exploits existing data signals on wiring and does not have to generate any signals itself. Noise-domain reflectometry, like time-domain and spread-spectrum time domain reflectometers, is most often used in identifying the location of wire faults in electrical lines.
Spread Spectrum Time Domain Vernier Method or SSTDV, is a time domain reflectometry method that uses a spread spectrum time domain reflectometry signal to locate intermittent faults in wires by measuring time delay between incident and reflected signals. SSTDR uses a pseudo noise (PN) code as the test signal. This code travels down the length of the wire, where it is reflected off of impedance discontinuities such as open or short circuits. The reflected signal is correlated with the incident signal to identify the locations of these discontinuities. In the case of SSTDV, the correlation is accomplished by adding one bit to the PN code each cycle, thus creating a vernier sequence that can be used to resolve the time delay between incident and reflected signals.
An arc fault is a high power discharge of electricity between two or more conductors. This discharge generates heat, which can break down the wire's insulation and trigger an electrical fire. Arc faults can range in current from a few amps up to thousands of amps, and are highly variable in strength and duration.
Rayleigh scattering based distributed acoustic sensing (DAS) systems use fiber optic cables to provide distributed strain sensing. In DAS, the optical fiber cable becomes the sensing element and measurements are made, and in part processed, using an attached optoelectronic device. Such a system allows acoustic frequency strain signals to be detected over large distances and in harsh environments.
Reflectometry uses the reflection of waves at surfaces and interfaces to detect or characterize objects.
A TDR moisture sensor employs time-domain reflectometry (TDR) to measure moisture content indirectly based on the correlation to electric and dielectric properties of materials, such as soil, agrarian products, snow, wood or concrete.
References
- ↑ Smith,Paul, Furse, Cynthia and Gunther, Jacob. "Analysis of Spread Spectrum Time Domain Reflectometry for Wire Fault Location." IEEE Sensors Journal. December, 2005. Archived February 12, 2011, at WebCite
- ↑ Smith,Paul, Furse, Cynthia, Safavi, Mehdi, and Lo, Chet. "Feasibility of Spread Spectrum Sensors for Location of Arcs on Live Wires Spread Spectrum Sensors for Location of Arcs on Live Wires." IEEE Sensors Journal. December, 2005. Archived February 12, 2011, at WebCite
- ↑ Smith,Paul, Furse, Cynthia, Chung Chung, You, Pendayala, Praveeen, Nagoti, Kedarnath and Lo, Chet. "Spread Spectrum TDR Research | Spread Spectrum Sensors for Wire Fault Location on Live Wire Networks | LiveWireTest.com Sensors for Critical Fault Location on Live Wires." IEEE Sensors Journal. June, 2005. Archived February 12, 2011, at WebCite