10. Quadrature-Amplitude Modulation

Quadrature-amplitude modulation (QAM)

It is a form of digital modulation where information is contained in both the amplitude and the phase of the transmitted carrier.

ASK and PSK

These are combined to create QAM.

TRUE

[TRUE or FALSE] Increasing the number of available symbols is a standard way to increase the bit rate, because increasing the number of symbols increases the number of bits per symbol.

8-QAM transmitter

8-QAM

16-QAM transmitter

QAM Formats and Bit Rates

TRUE

[TRUE or FALSE] The advantage of using QAM is that it is a higher order form of modulation—it is able to carry more bits of information per symbol.

TRUE

[TRUE or FALSE] By selecting a higher order format of QAM, the data rate of a link can be increased.

TRUE

[TRUE or FALSE] As the QAM order increases, so the distance between the different points on the constellation diagram decreases and there is a higher possibility of data errors being introduced.

ASK, FSK, PSK, and QAM Summary

efficient usage of bandwidth

The primary benefit of QAM variants

bits per carrier

The primary benefit of QAM variants is efficient usage of bandwidth. This is because QAM represents more ____. For example, 256-QAM maps 8 bits per carrier and 16-QAM maps 4 bits per carrier.

TRUE

[TRUE or FALSE] A disadvantage of QAM is that it is more susceptible to noise.

lower

QAM is more susceptible to noise. This is because the transmission states are close together and a ___ level of noise is required to move the signal from one point to another.

amplifiers

Unlike QAM systems, receivers equipped with phase or frequency modulation can limit ___ and remove amplitude noise.

receivers

Unlike QAM systems, ___ equipped with phase or frequency modulation can limit amplifiers and remove amplitude noise.

linearity

In a QAM system that contain an amplitude component, ____ must be maintained.

fall short

In a QAM system that contain an amplitude component, linearity must be maintained. Unfortunately, these linear amplifiers ____ when it comes to efficiency, and they consume more power.

QAM

It is widely used in the radio communications field because of the increase of the bit data rate.

QAM

It is used in applications ranging from short-range wireless communications to long-distance telephone systems.

QAM

It is used in microwave and telecommunication systems to transmit the information.

64 QAM and 256 QAM

They are used in digital cable television and cable modem.

QAM

It is used in optical fiber systems to increase bit rates.

QAM

It is used in many communication systems like Wi-Fi,, Digital Video Broadcast (DVB), and WiMAX.