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Topic: Quadrature amplitude modulation

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 What is Quadrature Amplitude Modulation?
More technically, quadrature amplitude modulation is a system of modulation in which data is transferred by modulating the amplitude of two separate carrier waves, mostly sinusoidal, which are out of phase by 90 degrees (sine and cosine).
In quadrature amplitude modulation, a signal obtained by summing the amplitude and phase modulation of a carrier signal (a modulated sine and cosine wave or quadrature waves) is used for the data transfer.
Incidentally, rectangular quadrature amplitude modulations are preferred to non-rectangular quadrature amplitude modulations as the former is easier to modulate and demodulate.
www.tech-faq.com /quadrature-amplitude-modulation.shtml   (516 words)

 Quadrature amplitude modulation - Wikipedia, the free encyclopedia
Quadrature amplitude modulation (QAM) is a modulation scheme which conveys data by changing (modulating) the amplitude of two carrier waves.
As with all modulation schemes, QAM conveys data by changing some aspect of a carrier signal, or the carrier wave, (usually a sinusoid) in response to a data signal.
Phase modulation (analogue PM) and phase-shift keying (digital PSK) can be regarded as a special case of QAM, where the amplitude of the modulating signal is constant, with only the phase varying.
en.wikipedia.org /wiki/Quadrature_amplitude_modulation   (1334 words)

 Definition: quadrature amplitude modulation   (Site not responding. Last check: 2007-10-12)
Quadrature modulation in which the two carriers are amplitude modulated.
Note 1: The name quadrature originates from the stipulation that a phase shift, when required, must be an integral multiple of p/2 radians, i.e., one-quarter of a cycle (unit interval, or baud).
In practice, the governing factors are the amplitude (and consequently, phase) stability, and the amount of noise present, in both the terminal equipment and the transmission medium (carrier frequency, or communication channel) involved.
www.atis.org /tg2k/_quadrature_amplitude_modulation.html   (269 words)

 Adaptive quadrature amplitude modulation decoding system - Patent 6680985
An adaptive quadrature amplitude modulation ("QAM") decoding system for use in, for example, high speed, bandwidth efficient QAM communication systems includes a circuit that adaptively adjusts gain and voltage bias and provides adaptive equalization feedback based on the same signal used to decode the QAM symbols.
Quadrature amplitude modulation ("QAM") is the most likely modulation technique to be able to reliably deliver data at such a high rate of transmission.
A quadrature amplitude modulation ("QAM") decoding circuit 9 constructed in accordance with the invention is shown in FIG.
www.freepatentsonline.com /6680985.html   (5180 words)

 Quadrature Amplitude Modulation   (Site not responding. Last check: 2007-10-12)
Quadrature amplitude modulation (QAM) is a modulation scheme in which two sinusoidal carriers, one exactly 90 degrees out of phase with respect to the other, are used to transmit data over a given physical channel.
QAM and its derivatives are used in both mobile radio and satellite communication systems.
Similarly, DPSK requires additional logic at the front end of the QAM modulator to generate the encoded data sequences to the I and Q inputs of the modulator.
www.altera.com /products/ip/altera/t-alt-qam.html   (542 words)

 Radio receivers for receiving both VSB and QAM digital HDTV signals - Patent 5715012
The carrier frequencies of the QAM and VSB final IF signals are regulated to be submultiples of the multiple of both the symbol frequencies of the QAM and VSB signals by applying automatic frequency and phase control signals developed in the digital circuitry to a local oscillator of the tuner.
Embodiments are disclosed in which the symbol frequencies of the QAM signal are respectively the twelfth, eleventh, tenth and ninth subharmonics of 43.04 MHz and the symbol frequencies of the VSB signal are respectively the thirty-sixth, twenty-eighth, twenty-second and eighteenth subharmonics of 43.04 MHz.
In a preferred such embodiment the symbol frequency of the QAM signal is the ninth subharmonic of 43.04 MHz and the symbol frequency of the VSB signal is the sixth subharmonic of 43.04 MHz.
www.freepatentsonline.com /5715012.html   (11147 words)

 QAM- Developer Zone - National Instruments
It is constructed using the principles of several forms of both analog and digital modulation techniques including amplitude modulation, phase-shift (digital keying) modulation, and the principles of clocking pulses.
QAM is a modulation process that incorporates the techniques of digital (coded) Phase Shift Keying (PSK) and digital (quantized) Amplitude Modulation.
The two quadrature signals are processed, then coded, and the resulting representative codes can be visualized as being placed on pedestals with different plus and minus amplitudes.
zone.ni.com /devzone/cda/tut/p/id/2659   (872 words)

 QAM Defined and Example Constellation Diagrams of Digital Signal Quality
In practice, there is always a combination of modulation errors that may be difficult to separate and identify, as such, it is recommended to evaluate the measured constellation diagrams using mathematical and statistically methods.
Amplitude Imbalance describes the different gains of the I and Q components of a signal.
Phase Jitter or phase noise in the QAM signal is caused by transponders in the transmission path or by the I/Q modulator.
www.blondertongue.com /QAM-Transmodulator/QAM_defined.php   (660 words)

 Quadrature Amplitude Modulation
(QAM) is the encoding of information into a carrier wave by variation of the amplitude of both the carrier wave and a 'quadrature' carrier that is 90° out of phase with the main carrier in accordance with two input signals.
QAM is used extensively in modems, and other forms of digital communication over analog channels.
In these applications, the modulating signal is generally quantized in both its in-phase and 90° components.
www.infomatek.com /quadrature_amplitude_modulation.htm   (193 words)

 Airlinx - QAM Quadrature Amplitude Modulation
Our success in QAM modulation is due to our broad set of core competencies in digital modem and radio design, and our commitment to bring true 10 Mbps full-duplex throughput to the 5.8 GHz ISM band.
Quadrature Amplitude Modulation varies both the amplitude and the phase of the signal.
uadrature Amplitude Modulation was developed to overcome the individual constraints of excessively complex AM or PM, by using a combination of the two simultaneously.
www.airlinx.com /details/QAMAirlinx.html   (709 words)

 Quadrature Amplitude Modulation - Stereo AM
As with all modulation schemes, QAM conveys data by changing some aspect of a base signal, the carrier wave, (usually a sinusoid) in response to a data signal.
In the case of QAM, the amplitude of two quadrature waves is changed (modulated or keyed) to represent the data signal.
Analogue QAM is used in NTSC and PAL television systems, where the I- and Q-signals carry the components of chroma (colour) information.
members.aol.com /StereoAM/quadrature-amplitude-modulation.html   (483 words)

 Selected Technologies
Quadrature amplitude modulation (QAM) is a multilevel vector modulation format in which both the amplitude and phase of the carrier signal are modulated.
QAM can achieve higher spectral efficiency than many other modulation formats and is, therefore, attractive in a densely populated signal environment.
First, optical amplitude modulation was used to transmit a 4 Gb/s QAM signal over a 105 km Raman-amplified link.
www.nrl.navy.mil /techtransfer/fs.php?fs_id=C07   (234 words)

 Quadrature Amplitude Modulation
The two modulation inputs (analog or digital) are applied to two separate balanced modulators (BM) each of which are supplied with the sin or cos carriers, i.e., modulator #1 is supplied with the sin carrier and modulator #2 is supplied with the cos carrier.
The outputs of both modulators are algebraically summed; the result of which is now a single signal to be transmitted, containing the I and Q information.
In the more recent incarnations of the QAM or I and Q modulation techniques, an Analog to Digital Convertor (ADC) is used to first convert the analog input to a serialized digital bit stream and is applied to the QAM modulators; likewise at the receiver.
www.williamson-labs.com /480_qam.htm   (310 words)

 ACRO.IT: QAM - Quadrature Amplitude Modulation
Operation of QAM is somewhat simple; it operates by modulating a carrier sine wave signal in amplitude and phase.
In QAM coding scheme each symbol is specific combination of signal amplitude and phase.
The effects of modulation were that the resulting signal was not the single frequency, but rather the range of frequencies.
www.acro.it /QAM.html   (295 words)

 QAM - Quadrature Amplitude Modulation   (Site not responding. Last check: 2007-10-12)
Modulation technique using two amplitude modulated RF (Radio Frequency) carriers that are out of phase by 90 degrees.
Information transfer is achieved using a mixture of phase and amplitude changes.
Since noise also appears as amplitude variations QAM is prone to interference.
www.mpirical.com /companion/Transmission/QAMModulation.htm   (42 words)

 Sunrise Telecom - CATV - T1 Seminars   (Site not responding. Last check: 2007-10-12)
To feed the cable system the bit stream is modulated using QAM modulation and then up-converted to a channel to be carrier on the cable system.
Quadrature Amplitude Modulation (QAM) is a modulation method that has been used in analog television since the beginning of color television.
QAM is a method of amplitude modulation that allows 2 channels of information to be transmitted at the same time on a particular frequency.
www.sunrisetelecom.com /broadband/ap_note_dvm.shtml   (2814 words)

 What is QAM? - a definition from Whatis.com - see also: quadrature amplitude modulation
- QAM (quadrature amplitude modulation) is a method of combining two amplitude-modulated (AM) signals into a single channel, thereby doubling the effective bandwidth.
In a QAM signal, there are two carriers, each having the same frequency but differing in phase by 90 degrees (one quarter of a cycle, from which the term quadrature arises).
The two modulated carriers are combined at the source for transmission.
searchnetworking.techtarget.com /sDefinition/0,,sid7_gci541804,00.html   (260 words)

 Amplitude Modulation - Stereo AM
Amplitude modulation (AM) is a form of modulation in which the amplitude of a carrier wave is varied in direct proportion to that of a modulating signal.
Its output is a signal at the carrier frequency, with peaks that trace the amplitude of the unmodulated signal.
In its basic form, amplitude modulation produces a signal with power concentrated at the carrier frequency and in two adjacent sidebands.
members.aol.com /StereoAM/amplitude-modulation.html   (629 words)

 Quadrature Amplitude Modulation - MythTV
It has been suggested that this article or section be merged into QAM.
Quadrature Amplitude Modulation is a method of encoding digital signals on a cable television system.
It is commonly used to transmit digital cable TV channels on the otherwise analog RF cables, and can be decoded (assuming the video signal is not encrypted), by several types of tuner cards.
www.mythtv.org /wiki/index.php/Quadrature_Amplitude_Modulation   (78 words)

 QAM and quadrature amplitude modulation and quadrature amplitude modulations
Quadrature amplitude modulation Golay complementary sequences for orthogonal frequency division multiplexing: (Dissertation)
Modulation using two carriers out of phase by 90° and modulated by separate signals.
It can modulate transport stream from ASI interface or Ethernet and output the IF or RF QAM signals after channel coding, interleaving, scrambling and quadrature modulation specified in DVB standards or directly output transport stream after PID filtrating.
www.etesters.com /search/product/listAll.cfm/keyword/QAM   (864 words)

 Quadrature - Wikipedia, the free encyclopedia
Quadrature amplitude modulation (QAM), a modulation method of using both a carrier wave and a 'quadrature' carrier wave that is 90° out of phase with the main carrier
Quadrature of the circle (also squaring the circle), in geometry, the problem of constructing a square and circle of equal area, impossible using only an unmarked straight-edge and compass
In astronomy, quadrature occurs when two celestial bodies appear 90° apart from one another as viewed from a third celestial body.
en.wikipedia.org /wiki/Quadrature   (288 words)

 Quadrature Amplitude Modulation   (Site not responding. Last check: 2007-10-12)
Quadrature amplitude modulation, or QAM, is a big name for a relatively simply technique.
It is simply a combination of amplitude modulation and phase shift keying.
We'll use a signal that is transmitting at 3600 bps, or 3 bits per baud.
www.physics.udel.edu /wwwusers/watson/student_projects/scen167/thosguys/qam.html   (174 words)

 QAM Simulation   (Site not responding. Last check: 2007-10-12)
Quadrature amplitude modulation (QAM) is one approach toward a
In this case, both the amplitude and the phase vary, so the points no longer lie on the
We have implemented a 16-QAM modulator- demodulator Demonstration in Simulink.
www.hait.ac.il /staff/commEng/Michael_Bank/qam/qam.html   (210 words)

 Amazon.fr : Quadrature Amplitude Modulation: From Basics To Adaptive Trellis-coded, Turbo-equalised And Space-time ...   (Site not responding. Last check: 2007-10-12)
QAM is a method for encoding digital data in an analog signal and continues to attract growing interest as it can offer the increased bandwidth necessary for future mobile multimedia communications.
Quadrature Amplitude Modulation continues to provide an all-encompassing self-contained treatment of single and multicarrier QAM based communications and will now maintain its attractiveness to a wide range of readers.
In addition, it also includes a fully revised chapter on adaptive modulation and a new chapter characterizing the design trade-offs of adaptive modulation and space-time coding.
www.amazon.fr /Quadrature-Amplitude-Modulation-Trellis-coded-Turbo-equalised/dp/0470094680   (609 words)

 Digital Cable Quadrature Amplitude Modulation (QAM)   (Site not responding. Last check: 2007-10-12)
Trellis Coded Modulation (TCM) is an encoder that selects an optimal sequence from the data stream and a map of the QAM constellation.
The constellation in TCM is usually larger than required for the data stream, and the encoder generates a sequence of wider words mapped such that the transition distances in the constellation are maximized.
The mapped data pairs are upconverted to an intermediate frequency before transmitting.The digital upconverter (DUC) translates signals from a baseband frequency to the intermediate frequency and the numerically controlled oscillator (NCO) is the key component for the DUC.
www.altera.com /end-markets/broadcast/delivery/qam/bro-qam.html   (617 words)

 QAM - Quadrature Amplitude Modulation   (Site not responding. Last check: 2007-10-12)
A modulation technique using variations in simple amplitude.
Every attempt has been made to provide you with the correct acronym for QAM.
If we missed the mark, we would greatly appreciate your help by entering the correct or alternate meaning in the box below.
www.auditmypc.com /acronym/QAM.asp   (102 words)

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