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Single-frequency Network
A single-frequency network or SFN is a broadcast network where several transmitters simultaneously send the same signal over the same frequency channel. Analog AM and FM radio broadcast networks as well as digital broadcast networks can operate in this manner. SFNs are not generally compatible with analog television transmission, since the SFN results in ghosting due to echoes of the same signal. A simplified form of SFN can be achieved by a low power co-channel repeater, booster or broadcast translator, which is utilized as a gap filler transmitter. The aim of SFNs is efficient utilization of the radio spectrum, allowing a higher number of radio and TV programs in comparison to traditional multi-frequency network (MFN) transmission. An SFN may also increase the coverage area and decrease the outage probability in comparison to an MFN, since the total received signal strength may increase to positions midway between the transmitters. SFN schemes are somewhat analogous to what ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Broadcast Network
A terrestrial network (or broadcast network in the United States) is a group of radio stations, television stations, or other electronic media outlets, that form an agreement to air, or broadcast, content from a centralized source. For example, (United States, U.S.), (Canada), the (United Kingdom, UK), the (Australia), (Germany), (South Korea), and NHK (Japan) are TV networks that provide television program, programming for local terrestrial television network affiliate, station affiliates to air using signals that can be picked up by the home television sets of local viewers. Networks generally, but not always, operate on a national scale; that is, they cover an entire country. Streaming media, Internet radio, and webcasting are sometimes considered forms of broadcasting despite the lack of terrestrial stations; its practitioners may also be called "broadcasters" or even "broadcast networks". American networks AT&T's "WEAF Chain" Following the Radio in the United St ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dynamic Single Frequency Network
{{Unreferenced, date=January 2008 Dynamic Single Frequency Networks (DSFN) is a transmitter macrodiversity technique for OFDM based cellular networks. DSFN is based on the idea of single frequency networks (SFN), which is a group of radio transmitters that send the same signal simultaneously over the same frequency. The term originates from the broadcasting world, where a broadcast network is a group of transmitters that send the same TV or radio program. Digital wireless communication systems based on the OFDM modulation scheme are well-suited to SFN operation, since OFDM in combination with some forward error correction scheme can eliminate intersymbol interference and fading caused by multipath propagation without the use of complex equalization. The concept of DSFN implies the SFN grouping is changed dynamically over time, from timeslot to timeslot. The aim is to achieve efficient spectrum utilization for downlink unicast or multicast communication services in centrally contro ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Guard Interval
In telecommunications, guard intervals are used to ensure that distinct transmissions do not interfere with one another, or otherwise cause overlapping transmissions. These transmissions may belong to different users (as in TDMA) or to the same user (as in OFDM). The purpose of the guard interval is to introduce immunity to propagation delays, echoes and reflections, to which digital data is normally very sensitive. Use in digital communications systems In OFDM, the beginning of each symbol is preceded by a guard interval. As long as the echoes fall within this interval, they will not affect the receiver's ability to safely decode the actual data, as data is only interpreted outside the guard interval. In TDMA, each user's timeslot ''ends'' with a guard interval. Thus, the guard interval protects against data loss within the same timeslot, and protects the following user's timeslot from interference caused by propagation delay. It is a common misconception that TDMA timeslo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Modulator
In electronics and telecommunications, modulation is the process of varying one or more properties of a periodic waveform, called the ''carrier signal'', with a separate signal called the ''modulation signal'' that typically contains information to be transmitted. For example, the modulation signal might be an audio signal representing sound from a microphone, a video signal representing moving images from a video camera, or a digital signal representing a sequence of binary digits, a bitstream from a computer. The carrier is higher in frequency than the modulation signal. In radio communication the modulated carrier is transmitted through space as a radio wave to a radio receiver. Another purpose is to transmit multiple channels of information through a single communication medium, using frequency-division multiplexing (FDM). For example in cable television which uses FDM, many carrier signals, each modulated with a different television channel, are transported through a sing ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
COFDM
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] |
OFDM
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] |
Self-interference Cancellation
Self-interference cancellation (SIC) is a signal processing technique that enables a radio transceiver to simultaneously transmit and receive on a single channel, a pair of partially-overlapping channels, or any pair of channels in the same frequency band. When used to allow simultaneous transmission and reception on the same frequency, sometimes referred to as “in-band full-duplex” or “simultaneous transmit and receive,” SIC effectively doubles spectral efficiency. SIC also enables devices and platforms containing two radios that use the same frequency band to operate both radios simultaneously. Self-interference cancellation has applications in mobile networks, the unlicensed bands, cable TV, mesh networks, the military, and public safety. In-band full-duplex has advantages over conventional duplexing schemes. A frequency division duplexing (FDD) system transmits and receives at the same time by using two (usually widely separated) channels in the same frequency band. In- ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Digital Broadcasting
Digital broadcasting is the practice of using digital signals rather than analogue signals for broadcasting over radio frequency bands. Digital television broadcasting (especially satellite television) is widespread. Digital audio broadcasting is being adopted more slowly for radio broadcasting where it is mainly used in Satellite radio. Digital links, thanks to the use of data compression, generally have greater spectral efficiency than analog links. Content providers can provide more services or a higher-quality signal than was previously available. It is estimated that the share of digital broadcasting increased from 7% of the total amount of broadcast information in 2000, to 25% in 2007. Some countries have completed a Digital television transition. See also *Digital radio *Digital television * ATSC Standards *ATSC tuner *Digital Audio Broadcasting *Digital Radio Mondiale *Digital Video Broadcasting *HD Radio *Satellite radio *Satellite television Satellite television is ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Equalization (communications)
In telecommunication, equalization is the reversal of distortion incurred by a signal transmitted through a Channel (communications), channel. Equalizers are used to render the frequency response—for instance of a telephone line—''flat'' from end-to-end. When a communication channel, channel has been equalized the frequency domain attributes of the signal at the input are faithfully reproduced at the output. Telephones, DSL lines and television cables use equalizers to prepare data signals for transmission. Equalizers are critical to the successful operation of electronic systems such as Analog television, analog broadcast television. In this application the actual waveform of the transmitted signal must be preserved, not just its frequency content. Equalizing filters must cancel out any group delay and phase delay between different frequency components. Analog telecommunications Audio lines Early telephone systems used equalization to correct for the reduced level of high ... [...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 Channel (communications), 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 different levels of fading and interference. 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 signal are transmitted at dif ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Intersymbol Interference
In telecommunication, intersymbol interference (ISI) is a form of distortion of a signal in which one symbol interferes with subsequent symbols. This is an unwanted phenomenon as the previous symbols have a similar effect as noise, thus making the communication less reliable. The spreading of the pulse beyond its allotted time interval causes it to interfere with neighboring pulses. ISI is usually caused by multipath propagation or the inherent linear or non-linear frequency response of a communication channel causing successive symbols to blur together. The presence of ISI in the system introduces errors in the decision device at the receiver output. Therefore, in the design of the transmitting and receiving filters, the objective is to minimize the effects of ISI, and thereby deliver the digital data to its destination with the smallest error rate possible. Ways to alleviate intersymbol interference include adaptive equalization and error correcting codes. Causes Multip ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Wideband
In communications, a system is wideband when the message bandwidth significantly exceeds the coherence bandwidth of the Channel (communications), channel. Some communication links have such a high Bit rate, data rate that they are forced to use a wide bandwidth Bandwidth commonly refers to: * Bandwidth (signal processing) or ''analog bandwidth'', ''frequency bandwidth'', or ''radio bandwidth'', a measure of the width of a frequency range * Bandwidth (computing), the rate of data transfer, bit rate or thr ...; other links may have relatively low data rates, but deliberately use a wider bandwidth than "necessary" for that data rate in order to gain other advantages; see ''spread spectrum''. A wideband Antenna (radio), antenna is one with approximately or exactly the same operating characteristics over a very wide Passband. It is distinguished from broadband antennas, where the passband is large, but the antenna gain and/or radiation pattern need not stay the same over the passband ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
