|
Underwater Acoustic Communication
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. 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 u ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Orthogonal Frequency-division Multiplexing
In telecommunications, orthogonal frequency-division multiplexing (OFDM) is a type of digital transmission and a method of encoding digital data on multiple carrier frequencies. OFDM has developed into a popular scheme for wideband digital communication, used in applications such as digital television and audio broadcasting, DSL internet access, wireless networks, power line networks, and 4G/ 5G mobile communications. OFDM is a frequency-division multiplexing (FDM) scheme that was introduced by Robert W. Chang of Bell Labs in 1966. In OFDM, multiple closely spaced orthogonal subcarrier signals with overlapping spectra are transmitted to carry data in parallel.webe.org - 2GHz BAS Relocation Tech-Fair, COFDM Technology Basics 2007-03-02 Demodula ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Telecommunications
Telecommunication is the transmission of information by various types of technologies over wire, radio, optical, or other electromagnetic systems. It has its origin in the desire of humans for communication over a distance greater than that feasible with the human voice, but with a similar scale of expediency; thus, slow systems (such as postal mail) are excluded from the field. The transmission media in telecommunication have evolved through numerous stages of technology, from beacons and other visual signals (such as smoke signals, semaphore telegraphs, signal flags, and optical heliographs), to electrical cable and electromagnetic radiation, including light. Such transmission paths are often divided into communication channels, which afford the advantages of multiplexing multiple concurrent communication sessions. ''Telecommunication'' is often used in its plural form. Other examples of pre-modern long-distance communication included audio messages, such as coded drumb ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Acoustic Communication In Fish
Fish are aquatic, craniate, gill-bearing animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Approximately 95% of living fish species are ray-finned fish, belonging to the class Actinopterygii, with around 99% of those being teleosts. The earliest organisms that can be classified as fish were soft-bodied chordates that first appeared during the Cambrian period. Although they lacked a true spine, they possessed notochords which allowed them to be more agile than their invertebrate counterparts. Fish would continue to evolve through the Paleozoic era, diversifying into a wide variety of forms. Many fish of the Paleozoic developed external armor that protected them from predators. The first fish with jaws appeared in the Silurian period, after which many (such as sharks) became formidable marine predators rather than just the prey of arthropods ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Acoustic Communication In Aquatic Animals
Communication occurs when an animal produces a signal and uses it to influences the behaviour of another animal. A signal can be any behavioural, structural or physiological trait that has evolved specifically to carry information about the sender and/or the external environment and to stimulate the sensory system of the receiver to change their behaviour. A signal is different from a cue in that cues are informational traits that have not been selected for communication purposes. For example, if an alerted bird gives a warning call to a predator and causes the predator to give up the hunt, the bird is using the sound as a signal to communicate its awareness to the predator. On the other hand, if a rat forages in the leaves and makes a sound that attracts a predator, the sound itself is a cue and the interaction is not considered a communication attempt. Air and water have different physical properties which lead to different velocity and clarity of the signal transmission proces ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Android (operating System)
Android is a mobile operating system based on a modified version of the Linux kernel and other open-source software, designed primarily for touchscreen mobile devices such as smartphones and tablets. Android is developed by a consortium of developers known as the Open Handset Alliance and commercially sponsored by Google. It was unveiled in November 2007, with the first commercial Android device, the HTC Dream, being launched in September 2008. Most versions of Android are proprietary. The core components are taken from the Android Open Source Project (AOSP), which is free and open-source software (FOSS) primarily licensed under the Apache License. When Android is installed on devices, the ability to modify the otherwise free and open-source software is usually restricted, either by not providing the corresponding source code or by preventing reinstallation through technical measures, thus rendering the installed version proprietary. Most Android devices ship with additional ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Janus
In ancient Roman religion and myth, Janus ( ; la, Ianvs ) 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 a building in Rome named after him (not a temple, as it is often called, but an open enclosure with gates at each end) 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)'' a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Standardization Agreement
In NATO, a standardization agreement (STANAG, 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 communication technology standards. STANAGs are published in English and French, the two official languages of NATO, by the NATO Standardization Office in Bru ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Modem
A modulator-demodulator or modem is a computer hardware device that converts data from a digital format into a format suitable for an analog transmission medium such as telephone or radio. A modem transmits data by Modulation#Digital modulation methods, modulating one or more carrier wave signals to encode digital information, while the receiver Demodulation, demodulates the signal to recreate the original digital information. The goal is to produce a Signal (electronics), signal that can be transmitted easily and decoded reliably. Modems can be used with almost any means of transmitting analog signals, from light-emitting diodes to radio. Early modems were devices that used audible sounds suitable for transmission over traditional telephone systems and leased lines. These generally operated at 110 or 300 bits per second (bit/s), and the connection between devices was normally manual, using an attached telephone handset. By the 1970s, higher speeds of 1,200 and 2,400 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Centre For Maritime Research And Experimentation
Directed by Dr Catherine Warner, the Centre for Maritime Research and Experimentation (CMRE) is an established, world-class scientific research and experimentation facility that organizes and conducts scientific research and technology development, centred on the maritime domain, delivering innovative and field-tested Science & Technology (S&T) solutions to address defence and security needs of NATO. The CMRE is an executive body of NATO's Science and Technology Organization (STO) along with the NATO Collaboration Support Office and Office of the Chief Scientist (OCS). Located in La Spezia (Italy), the CMRE is built on more than 60 years of experience in its former establishments as the NATO Undersea Research Centre (NURC) and SACLANTCEN and has produced a cadre of leaders in ocean science, modelling and simulation, acoustics and other disciplines, as well as producing critical results and understanding that have been built into the operational concepts of NATO and the Natio ... [...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 nonlinear signal-processing device such as a vacuum tube, transistor, or diode, usually called a '' 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 filtered out of the output of the mixer. Heterodyne frequencies are related to the phenomenon of "beats" in acoustics. A major a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Submersible
A submersible is a small watercraft designed to operate underwater. The term "submersible" is often used to differentiate from other underwater vessels known as submarines, in that a submarine is a fully self-sufficient craft, capable of independent cruising with its own power supply and air renewal system, whereas a submersible is usually supported by a nearby ship, surface vessel, very large floating structure, platform, shore team or sometimes a larger submarine. In common usage by the general public, however, the word "submarine" may be used to describe a craft that is by the technical definition actually a submersible. There are many types of submersibles, including both crewed and uncrewed craft, otherwise known as remotely operated vehicles (ROVs) or unmanned underwater vehicles (UUVs). Submersibles have many uses worldwide, such as oceanography, underwater archaeology, ocean exploration, adventure, equipment maintenance and recovery, and underwater videography. Histo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
