QAM

(redirected from 4QAM)

QAM

(communications)
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

QAM

In Q, or basic telecommunication code, it means, “What is the latest met (weather)?”

(1)

QAM

(2)
Quality Assurance Management.

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 effective throughput range is given by [eta]= {0,1,1.5, 2, 3, 4, 5} bits per symbol (BPS) when there is no-transmission, 4QAM, 8QAM, 16QAM, 32QAM, 64QAM and 256QAM are considered, respectively.
Suppose we have a 2 x 2 SM system with 4QAM modulation; thus the search tree has 4 layers and 8 branches.
And when K = L = 2, the modulation is 4QAM, that is, to design and implement 4QAM backscatter modulator, four RC lumped impedances are connected to an antenna port through RF 4-1 Mux, each lumped impedance corresponding to different reflection coefficients.
Considering 4QAM and accounting for all possible symbol combinations in the 1x3-dimensional [G.sup.n] vectors, there are a total of [N.sub.SG] = 16 conditional [mathematical expression not reproducible] subgroup sequences for m = 1, 2, 3, 4 with no "other" subgroup formed.
In this paper, 128 and 256 subcarriers have been taken for 4QAM and 16QAM modulation schemes and for each case, the effect of changing phase sequences on PAPR reduction and the BER performances considering AWGN channel have been observed.
Uplink Transmission Scheme PAPR [dB] 4QAM 16QAM 64QAM OFDMA 10.7 10.7 10.7 LFDMA 7.5 8.5 8.7 SLM-LFDMA 5.9 6.6 6.8 PTS-LFDMA 4.7 5.6 5.8
It is assumed that 1110 is the data sequence to transmit after local data flow and modulation is 4QAM. According to our proposed approach, only bits 11 will be modulated using 4QAM and transmitted via the corresponding antenna 10 while the bits 10 as the antenna index will be detected at the receiver.
The BER performance of adaptive modulation system was better than the most robust modulation mode 4QAM systems in terms of BER performance.
The corresponding modulations are no modulation, 4QAM, 16QAM, 64QAM, and 256QAM.
3, we plot the theoretical average BER and corresponding simulation of DAS with different receive antennas and modulation modes, where standard deviation [sigma] = 8dB, path loss exponent [beta]= [[beta].sub.i] = 3, BPSK and 4QAM are used for the system modulation.
In our simulations, the source signal is a binary sequence following the discrete uniform distribution and it is then modulated by 4QAM. All the channels are generated as i.i.d.

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