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Antenna Combining
Diversity combining is the technique applied to combine the multiple received signals of a diversity reception device into a single improved signal. Various techniques Various diversity combining techniques can be distinguished: * Equal-gain combining: All the received signals are summed coherently. * Maximal-ratio combining is often used in large phased-array systems: The received signals are weighted with respect to their SNR and then summed. The resulting SNR yields \sum_^SNR_k where SNR_k is SNR of the received signal k. * Switched combining: The receiver switches to another signal when the currently selected signal drops below a predefined threshold. This is also often called "Scanning Combining". * Selection combining: Of the N received signals, the strongest signal is selected. When the N signals are independent and Rayleigh distributed, the expected diversity gain has been shown to be \sum_^\frac, expressed as a power ratio. Therefore, any additional gain diminishes rap ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Diversity Scheme
In telecommunications, a diversity scheme refers to a method for improving the reliability of a message signal by using two or more communication channels with different characteristics. Diversity is mainly used in radio communication and is a common technique for combatting fading and co-channel interference and avoiding error bursts. It is based on the fact that individual channels experience fades and interference at different, random times, i.e., they are at least partly independent. Multiple versions of the same signal may be transmitted and/or received and combined in the receiver. Alternatively, a redundant forward error correction code may be added and different parts of the message transmitted over different channels. Diversity techniques may exploit the multipath propagation, resulting in a diversity gain, often measured in decibels. Diversity techniques The following classes of diversity schemes can be identified: * Time diversity: Multiple versions of the same si ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Diversity System Diagram
Diversity, diversify, or diverse may refer to: Business *Diversity (business), the inclusion of people of different identities (ethnicity, gender, age) in the workforce * Diversity marketing, marketing communication targeting diverse customers *Supplier diversity, the use of diverse suppliers *Team diversity Politics * Diversity (politics), the political and social policy of encouraging tolerance for people of different cultural and racial backgrounds * Diversity Immigrant Visa or Green Card Lottery, a United States immigration program * Diversity jurisdiction, a concept under which U.S. federal courts can hear suits between parties from different states * Diversity training, the process of educating people to function in a diverse environment * Cultural diversity, the respect of different cultures and interculturality * Functional diversity (disability), a term for special needs, disability, impairment and handicap * Gerodiversity, a multicultural approach to issues of aging * ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Transmit Diversity
Transmit diversity is the use of multiple transmit antennas to achieve reliability in radio communication. It involves using signals that originate from two or more independent sources that have been modulated with identical information-bearing signals and that may vary in their transmission characteristics at any given instant. It can help overcome the effects of fading, outages, and circuit failures. When using diversity transmission and reception, the amount of received signal improvement depends on the independence of the fading characteristics of the signal as well as circuit outages and failures. Considering antenna diversity, in many systems additional antennas may be expensive or impractical at the remote or even at the base station. In these cases, transmit diversity can be used to provide diversity benefit at a receiver with multiple transmit antennas only. With transmit diversity, multiple antennas transmit delayed versions of a signal, creating frequency-selective ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ambient Noise Level
In atmospheric sounding and noise pollution, ambient noise level (sometimes called background noise level, reference sound level, or room noise level) is the background sound pressure level at a given location, normally specified as a reference level to study a new intrusive sound source. Ambient sound levels are often measured in order to map sound conditions over a spatial regime to understand their variation with locale. In this case the product of the investigation is a sound level contour map. Alternatively ambient noise levels may be measured to provide a reference point for analyzing an intrusive sound to a given environment. For example, sometimes aircraft noise is studied by measuring ambient sound without presence of any overflights, and then studying the noise addition by measurement or computer simulation of overflight events. Or roadway noise is measured as ambient sound, prior to introducing a hypothetical noise barrier intended to reduce that ambient nois ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Los Angeles, California
Los Angeles, often referred to by its initials L.A., is the List of municipalities in California, most populous city in the U.S. state of California, and the commercial, Financial District, Los Angeles, financial, and Culture of Los Angeles, cultural center of Southern California. With an estimated 3,878,704 residents within the city limits , it is the List of United States cities by population, second-most populous in the United States, behind only New York City. Los Angeles has an Ethnic groups in Los Angeles, ethnically and culturally diverse population, and is the principal city of a Metropolitan statistical areas, metropolitan area of 12.9 million people (2024). Greater Los Angeles, a combined statistical area that includes the Los Angeles and Riverside–San Bernardino metropolitan areas, is a sprawling metropolis of over 18.5 million residents. The majority of the city proper lies in Los Angeles Basin, a basin in Southern California adjacent to the Pacific Ocean in the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
San Rafael, California
San Rafael ( ; Spanish language, Spanish for "Raphael (archangel), St. Raphael", ) is a city in and the county seat of Marin County, California, United States. The city is located in the North Bay (San Francisco Bay Area), North Bay region of the San Francisco Bay Area. As of the 2020 United States census, 2020 U.S. census, the city's population was 61,271, up from 57,713 in 2010. San Rafael was founded by the Spanish in 1817, when Vicente Francisco de Sarría established Mission San Rafael Arcángel, initially as an Asistencias, ''asistencia'' (sub-mission). San Rafael Arcángel was upgraded to full Spanish missions in California, mission status in 1822, a month before Alta California declared independence from Spain as part of First Mexican Empire, Mexico. Following the American Conquest of California, the community of San Rafael incorporated as a city in 1874. History San Rafael was once the site of several Coast Miwok villages: ''Awani-wi'', near downtown San Rafael, ''Ewu'' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Selective Calling
In a conventional, analog two-way radio system, a standard radio has ''noise squelch'' or ''carrier squelch'', which allows a radio to receive all transmissions. Selective calling is used to address a subset of all two-way radios on a single radio frequency channel. Where more than one user is on the same channel (co-channel users), selective calling can address a subset of all receivers or can direct a call to a single radio. Selective calling features fit into two major categories—''individual calling'' and ''group calling''. Individual calls generally have longer time-constants: it takes more air-time to call an individual radio unit than to call a large group of radios. Selective calling is akin to the use of a lock on a door. A radio with carrier squelch is unlocked and will let any signal in. Selective calling locks out all signals except ones with the correct "key", in this case a specific digital code. Selective calling systems can overlap; e.g. a radio may have CTCSS ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Oklahoma City, Oklahoma
Oklahoma City (), officially the City of Oklahoma City, and often shortened to OKC, is the List of capitals in the United States, capital and List of municipalities in Oklahoma, most populous city of the U.S. state of Oklahoma. The county seat of Oklahoma County, Oklahoma, Oklahoma County, its population ranks List of United States cities by population, 20th among United States cities and 8th in the Southern United States. The population grew following the 2010 Census and reached 681,054 in the 2020 United States census. The Oklahoma City metropolitan area had a population of 1,396,445, and the Oklahoma City–Shawnee, Oklahoma, Shawnee Combined Statistical Area had a population of 1,469,124, making it Oklahoma's largest municipality and metropolitan area by population. Oklahoma City's city limits extend somewhat into Canadian County, Oklahoma, Canadian, Cleveland County, Oklahoma, Cleveland, and Pottawatomie County, Oklahoma, Pottawatomie counties. However, much of those areas ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Signal Strength
In telecommunications, particularly in radio frequency engineering, signal strength is the transmitter power output as received by a reference antenna at a distance from the transmitting antenna. High-powered transmissions, such as those used in broadcasting, are measured in dB- millivolts per metre (dBmV/m). For very low-power systems, such as mobile phones, signal strength is usually expressed in dB- microvolts per metre (dBμV/m) or in decibels above a reference level of one milliwatt ( dBm). In broadcasting terminology, 1 mV/m is 1000 μV/m or 60 dBμ (often written dBu). Examples *100 dBμ or 100 mV/m: blanketing interference may occur on some receivers *60 dBμ or 1.0 mV/m: frequently considered the edge of a radio station's protected area in North America *40 dBμ or 0.1 mV/m: the minimum strength at which a station can be received with acceptable quality on most receivers Relationship to average radiated power The electric field strength at a specific point ca ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Microwave Radio Relay
Microwave transmission is the Data transmission, transmission of information by electromagnetic waves with wavelengths in the microwave frequency range of 300 MHz to 300 GHz (1 m - 1 mm wavelength) of the electromagnetic spectrum. Microwave signals are normally limited to the line of sight, so long-distance transmission using these signals requires a series of repeaters forming a microwave relay network. It is possible to use microwave signals in over-the-horizon communications using tropospheric scatter, but such systems are expensive and generally used only in specialist roles. Although an experimental microwave telecommunication link across the English Channel was demonstrated in 1931, the development of radar in World War II provided the technology for practical exploitation of microwave communication. During the war, the British Army introduced the Wireless Set No. 10, which used microwave relays to multiplexing, multiplex eight telephone channels over long ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Digital Signal 1
Digital Signal 1 (DS1, sometimes DS-1) is a T-carrier signaling scheme devised by Bell Labs. DS1 is the primary digital telephone standard used in the United States, Canada and Japan and is able to transmit up to 24 multiplexed voice and data calls over telephone lines. E-carrier is used in place of T-carrier outside the United States, Canada, Japan, and South Korea. DS1 is the logical bit pattern used over a physical T1 line; in practice, the terms ''DS1'' and ''T1'' are often used interchangeably. Overview T1 refers to the primary digital telephone carrier system used in North America. T1 is one line type of the PCM T-carrier hierarchy. T1 describes the cabling, signal type, and signal regeneration requirements of the carrier system. The signal transmitted on a T1 line, referred to as the DS1 signal, consists of serial bits transmitted at the rate of 1.544 Mbit/s. The type of line code used is called Alternate Mark Inversion (AMI). Digital Signal Designation is the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Frequency Modulation
Frequency modulation (FM) is a signal modulation technique used in electronic communication, originally for transmitting messages with a radio wave. In frequency modulation a carrier wave is varied in its instantaneous frequency in proportion to a property, primarily the instantaneous amplitude, of a message signal, such as an audio signal. The technology is used in telecommunications, radio broadcasting, signal processing, and Run-length limited#FM: .280.2C1.29 RLL, computing. In Analog signal, analog frequency modulation, such as radio broadcasting of voice and music, the instantaneous frequency deviation, i.e. the difference between the frequency of the carrier and its center frequency, has a functional relation to the modulating signal amplitude. Digital data can be encoded and transmitted with a type of frequency modulation known as frequency-shift keying (FSK), in which the instantaneous frequency of the carrier is shifted among a set of frequencies. The frequencies m ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
