QAM

(redirected from 4QAM)

QAM

QAM

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

QAM

(1)

QAM

(2)
Quality Assurance Management.

QAM

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

(2) (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.
References in periodicals archive ?
En este trabajo se consignan los resultados con modulacion 4QAM, dado que el interes del trabajo fue comparar el desempeno de algoritmos de diversas tecnicas de deteccion en MIMO y especialmente en L-MIMO, el uso de este toolbox de computacion paralela acelero la obtencion de resultados, y aunque los valores puntuales seguramente cambiaran en implementaciones reales por la diferencia en las estructuras de datos y el manejo del agendamiento de procesos, entre otros, la tendencia en el desempeno de los algoritmos que permite proyectar el orden en que mejor realizan la deteccion, se deberia mantener.
2014) y se soporto en el trabajo de Cespedes, Olmos, Sanchez-Fernandez, & Perez-Cruz, 2014, contemplando el modelo de canal MIMO en la misma forma que se establecio en este articulo pero trabajando con modulacion 4QAM para efectos de evaluacion comparativa con TS y las tecnicas de deteccion lineales y sus modos SIC presentadas con su respectiva fundamentacion matematica de la seccion 2.
The corresponding modulations are no modulation, 4QAM, 16QAM, 64QAM, and 256QAM.
The BER performance of adaptive modulation system was better than the most robust modulation mode 4QAM systems in terms of BER performance.
Specifically, for low SNR values from (1-10 dB), the throughput performance is similar to 4QAM.
Data is differentiated from 4QAM to 256QAM depending on transmission volume.
i] = 3, BPSK and 4QAM are used for the system modulation.
4 shows the BER performance of DAS with two receive antennas and different path loss exponents, where [sigma]=10dB, 4QAM and BPSK are used.
With 16QAM modulation, AirStar provides 56 Mbps of duplex capacity per channel while consuming only 14 MHz of spectrum in the upstream and downstream directions, enabling the operator to meet the service demands of the highest density urban districts, while still maintaining the ability to use 4QAM modulation to optimize coverage economics for lower density areas.
In our simulations, the source signal is a binary sequence following the discrete uniform distribution and it is then modulated by 4QAM.