Quadrature Amplitude Modulation


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quadrature amplitude modulation

[¦kwäd·rə·chər ‚am·plə‚tüd ‚mäj·ə′lā·shən]
(communications)
Abbreviated QAM.
Quadrature modulation in which the two carrier components are amplitude-modulated.
A digital modulation technique in which digital information is encoded in bit sequences of specified length and these bit sequences are represented by discrete amplitude levels of an analog carrier, by a phase shift of the analog carrier from the phase that represented the previous bit sequence by a multiple of 90°, or by both.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

Quadrature Amplitude Modulation

(QAM) A method for encoding digital data in an analog signal in which each combination of phase and amplitude represents one of sixteen four bit patterns. This is required for fax transmission at 9600 bits per second.
This article is provided by FOLDOC - Free Online Dictionary of Computing (foldoc.org)

QAM

(1) (Quality Assessment Measurement) A system used to measure and analyze voice transmission.

(2) (Quantum Abstract Machine) An interface from Rigetti Computing for running programs in a hybrid classical/quantum computer environment. See QVM and quantum computing.

(3) (Quadrature Amplitude Modulation) A modulation technique that employs both phase modulation (PM) and amplitude modulation (AM). Widely used to transmit digital signals such as digital cable TV and cable Internet service, QAM is also used as the modulation technique in orthogonal frequency division multiplexing (see OFDM). The "quadrature" comes from the fact that the phase modulation states are 90 degrees apart from each other.

Analog QAM
Analog QAM uses two carriers 90 degrees out of phase with each other. Each carrier is modulated by an analog signal, and the resulting modulated waves are combined (see example below).

Digital QAM
In digital QAM, the number of modulation states determines how the digital signal is split up. For example, in 8QAM, each three bits of input alters the phase and amplitude of the carrier to derive eight unique modulation states (see example below).

In 16QAM, 32QAM, 64QAM, 128QAM, 256QAM, 512QAM and 1024QAM, from four to 10 bits generate from 16 to 1,024 modulation states respectively. See modulation and binary values.


Analog QAM
Analog QAM modulates two carriers 90 degrees out of phase with each from two analog input streams. The modulated carriers are combined and transmitted.







Digital QAM (8QAM)
In 8QAM, three input bits generate eight modulation states using four phase angles on 90 degree boundaries and two amplitudes (4 phases X 2 amplitudes = 8 states). Digital modulation greater than 8QAM is difficult to visualize.







Quadrature PSK (QPSK)
QPSK is like 4QAM without amplitude modulation. QPSK uses four phase angles to represent each two bits of input; however, the amplitude remains constant.
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References in periodicals archive ?
The STi5197L includes a QAM (quadrature amplitude modulation) cable demodulator and is software compatible with, and shares the same architecture as, ST's popular STi5197 chip.
This LTE eNodeB is able to fully support a downlink rate of up to 150 Mbps in commercial LTE networks.By adopting 64QAM (Quadrature Amplitude Modulation) and MIMO (Multiple Input Multiple Output) technology with 2T2R (two transmitters and two receivers) capabilities, Huawei's latest LTE eNodeB is able to maximize the use of the ultra-wide bandwidth of LTE networks.
Modular CMTS is designed to economically increase DOCSIS capacity by separating MAC (media access control) routing and DOCSIS signaling, from the edge QAM (quadrature amplitude modulation), with each performed on purpose- designed platforms.
Additionally, the BigBand BMR provides QAM (quadrature amplitude modulation), which is designed to efficiently deliver digital video programming with compatibility to subscribers' access devices.
Quadrature amplitude modulation; from basics to adaptive trellis-coded, turbo-equalised and space-time coded OFDM, CDMA and MC-CDMA systems, 2d ed.
Modern mobile communication systems use band-limited linear modulation schemes, such as multi-level quadrature amplitude modulation (QAM) and quadrature phase shift keying (QPSK), which have high peak-to-average power ratio characteristics.
NAA/NSC member WSNet announced that it now offers its network of multiple dwelling unit (MDU) service providers digital video via Quadrature Amplitude Modulation (QAM), one of the most cost-effective methods of providing 200 channels of digital satellite television to apartment complexes, condominiums, townhomes, retirement communities, nursing homes, marinas, RV parks, university dormitories and new housing developments.
One popular scheme, known as discrete multitone (DMT), is a variation of the quadrature amplitude modulation line code widely used in analog modems.
Furthermore, the technology supports 4x4 MIMO (Multiple-Input, Multiple- Output) and higher-order 256 QAM (Quadrature amplitude modulation) scheme to maximize the data transfer rate.
Especially in modulation system, the quadrature oscillator is used to generate the carrier signal for quadrature amplitude modulation (QAM) and single-sideband modulation (SSB) [1,2].
According to the companies, this test, which was conducted across 2,200 kilometres of Segment F of the Reach North Asia Loop (RNAL), included Polarisation Multiplexed 8 Quadrature Amplitude Modulation (PM-8QAM) and a range of advanced FlexCoherent modulation formats, along with transmitter and receiver-based signal processing technologies.