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Wireless Diver Communications
Underwater acoustic communication is a technique of sending and receiving messages in 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. At the beginning of the 20th century some ships communicated by underwater bells as well as using the system for navigation. Submarine signals were at the time competitive with the primitive maritime radionavigation. The later Fessenden oscillator allowed communication with submarines. Types of modulation used for underwater acoustic communications In general the modulation methods developed for radio communications can be adapted for underwat ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Continuous Phase Modulation
Continuous phase modulation (CPM) is a method for modulation of data commonly used in wireless modems. In contrast to other coherent digital phase modulation techniques where the carrier phase abruptly resets to zero at the start of every symbol (e.g. M- PSK), with CPM the carrier phase is modulated in a continuous manner. For instance, with QPSK the carrier instantaneously jumps from a sine to a cosine (i.e. a 90 degree phase shift) whenever one of the two message bits of the current symbol differs from the two message bits of the previous symbol. This discontinuity requires a relatively large percentage of the power to occur outside of the intended band (e.g., high fractional out-of-band power), leading to poor spectral efficiency. Furthermore, CPM is typically implemented as a constant-envelope waveform, i.e., the transmitted carrier power is constant. Therefore, CPM is attractive because the phase continuity yields high spectral efficiency, and the constant envelope yields exc ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
JSON
JSON (JavaScript Object Notation, pronounced or ) is an open standard file format and electronic data interchange, data interchange format that uses Human-readable medium and data, human-readable text to store and transmit data objects consisting of name–value pairs and array data type, arrays (or other serialization, serializable values). It is a commonly used data format with diverse uses in electronic data interchange, including that of web applications with server (computing), servers. JSON is a Language-independent specification, language-independent data format. It was derived from JavaScript, but many modern programming languages include code to generate and parse JSON-format data. JSON filenames use the extension .json. Douglas Crockford originally specified the JSON format in the early 2000s. Transcript: He and Chip Morningstar sent the first JSON message in April 2001. Naming and pronunciation The 2017 international standard (ECMA-404 and ISO/IEC 21778:2017) ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Janus
In ancient Roman religion and myth, Janus ( ; ) is the god of beginnings, gates, transitions, time, duality, doorways, passages, frames, and endings. He is usually depicted as having two faces. The month of January is named for Janus (''Ianuarius''). According to ancient Roman farmers' almanacs, Juno was mistaken as the tutelary deity of the month of January, but Juno is the tutelary deity of the month of June. Janus presided over the beginning and ending of conflict, and hence war and peace. The gates of the Temple of Janus in Rome were opened in time of war and closed to mark the arrival of peace. As a god of transitions, he had functions pertaining to birth and to journeys and exchange, and in his association with Portunus, a similar harbor and gateway god, he was concerned with travelling, trading, and shipping. Janus had no flamen or specialised priest ''( sacerdos)'' assigned to him, but the King of the Sacred Rites ''( rex sacrorum)'' himself carried out his cerem ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Standardization Agreement
In NATO, a standardization agreement (STANAG, redundant acronym, redundantly: STANAG agreement) defines processes, procedures, terms, and conditions for common military or technical procedures or equipment between the member countries of the alliance. Each NATO state ratifies a STANAG and implements it within its own military. The purpose is to provide common operational and administrative procedures and logistics, so one member nation's military may use the stores and support of another member's military. STANAGs also form the basis for technical interoperability between a wide variety of communication and information systems (CIS) essential for NATO and Allied operations. The Allied Data Publication 34 (ADatP-34) NATO Interoperability Standards and Profiles which is covered by STANAG 5524, maintains a catalogue of relevant Information and communications technology, information and communication technology standards. STANAGs are published in English language, English and French ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Modem
The Democratic Movement (, ; MoDem ) is a centre to centre-right political party in France, whose main ideological trends are liberalism and Christian democracy, and that is characterised by a strong pro-Europeanist stance. MoDem was established by François Bayrou to succeed the Union for French Democracy (UDF) and contest the 2007 legislative election, after his strong showing in the 2007 presidential election. Initially named the Democratic Party (''Parti démocrate''), the party was renamed "Democratic Movement", because there was already a small Democratic Party in France. MoDem secured an agreement with La République En Marche! (LRM) — later Renaissance (RE) — in the 2017 legislative election after Bayrou had endorsed the candidacy of Emmanuel Macron in February. The two parties have since been in alliance, as of late named Ensemble. The party's founder and leader Bayrou has served as Prime Minister of France since December 2024. History Background MoDem tr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Centre For Maritime Research And Experimentation
Previously known as NATO Undersea Research Centre (NURC), the Centre for Maritime Research and Experimentation (CMRE) is a scientific research and experimentation NATO facility that organises and conducts scientific research and technology development, centred on the maritime domain, to address defence and security needs of the Alliance. It is an executive body of NATO Science and Technology Organization (STO). It was established in 1959. Research areas CMRE conducts projects in the following major research areas: *Littoral intelligence, surveillance and reconnaissance * Autonomous surveillance *Port and ship protection *Maritime situational awareness *Robotic/Intelligent preparation of the battlespace *Active sonar risk mitigation Organisation CMRE employs scientists and support staff from NATO member nations. Scientists rotate through the centre on a contract basis with a fixed time limit (typically three years with a possible two-year extension). As of December 2023, the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Heterodyne
A heterodyne is a signal frequency that is created by combining or mixing two other frequencies using a signal processing technique called ''heterodyning'', which was invented by Canadian inventor-engineer Reginald Fessenden. Heterodyning is used to shift signals from one frequency range into another, and is also involved in the processes of modulation and demodulation. The two input frequencies are combined in a linear circuit, nonlinear signal-processing device such as a vacuum tube, transistor, or diode, usually called a ''frequency mixer, mixer''. In the most common application, two signals at frequencies and are mixed, creating two new signals, one at the sum of the two frequencies , and the other at the difference between the two frequencies . The new signal frequencies are called ''heterodynes''. Typically, only one of the heterodynes is required and the other signal is filter (signal processing), filtered out of the output of the mixer. Heterodyne frequencies are rela ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Submersible
A submersible is an underwater vehicle which needs to be transported and supported by a larger ship, watercraft or dock, platform. This distinguishes submersibles from submarines, which are self-supporting and capable of prolonged independent operation at sea. There are many types of submersibles, including both human-occupied vehicles (HOVs) and uncrewed craft, variously known as remotely operated vehicles (ROVs) or unmanned underwater vehicles (UUVs). Submersibles have many uses including oceanography, underwater archaeology, ocean exploration, tourism, underwater work, equipment maintenance and underwater search and recovery, recovery and underwater videography. History The first recorded self-propelled underwater vessel was a small oar-powered submarine conceived by William Bourne (mathematician), William Bourne (c. 1535 – 1582) and designed and built by Dutch inventor Cornelis Drebbel in 1620, with two more improved versions built in the following four years.Konstam (201 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Joint Electronics Type Designation System
The Joint Electronics Type Designation System (JETDS), which was previously known as the Joint Army-Navy Nomenclature System (AN System. JAN) and the Joint Communications-Electronics Nomenclature System, is a method developed by the U.S. War Department during World War II for assigning an unclassified designator to electronic equipment. In 1957, the JETDS was formalized in MIL-STD-196. Computer software and commercial unmodified electronics for which the manufacturer maintains design control are not covered. Applicability Electronic material, from a military point of view, generally includes those electronic devices employed in data processing, detection and tracking (underwater, sea, land-based, air and space), recognition and identification, communications, aids to navigation, weapons control and evaluation, flight control, and electronics countermeasures. The JETDS applies to equipment throughout the DoD and select NATO allies today. Nomenclature is assigned to: * Electronic ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Phase Shifts
In physics and mathematics, the phase (symbol φ or ϕ) of a wave or other periodic function F of some real variable t (such as time) is an angle-like quantity representing the fraction of the cycle covered up to t. It is expressed in such a scale that it varies by one full turn as the variable t goes through each period (and F(t) goes through each complete cycle). It may be measured in any angular unit such as degrees or radians, thus increasing by 360° or 2\pi as the variable t completes a full period. This convention is especially appropriate for a sinusoidal function, since its value at any argument t then can be expressed as \varphi(t), the sine of the phase, multiplied by some factor (the amplitude of the sinusoid). (The cosine may be used instead of sine, depending on where one considers each period to start.) Usually, whole turns are ignored when expressing the phase; so that \varphi(t) is also a periodic function, with the same period as F, that repeatedly scans ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gaussian Filter
In electronics and signal processing, mainly in digital signal processing, a Gaussian filter is a filter (signal processing), filter whose impulse response is a Gaussian function (or an approximation to it, since a true Gaussian response would have infinite impulse response). Gaussian filters have the properties of having no Overshoot (signal), overshoot to a step function input while minimizing the rise and fall time. This behavior is closely connected to the fact that the Gaussian filter has the minimum possible group delay. A Gaussian filter will have the best combination of suppression of high frequencies while also minimizing spatial spread, being the critical point of the Fourier transform#Uncertainty principle, uncertainty principle. These properties are important in areas such as Oscilloscope#The vertical amplifier, oscilloscopes and digital telecommunication systems. Mathematically, a Gaussian filter modifies the input signal by convolution with a Gaussian function; thi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
