Quadrature Amplitude Modulation

In the amplitude modulation scheme, we can modulate one message signal (input signal) which is in analog form. It means we can give only one input signal and we can modulate it and transmit to the destination level. And the effective utilization of channel bandwidth is not up to the level. So, these can be overcome by this QAM technique. This article discusses what is quadrature amplitude modulation, its definition, block diagram, working principle, and it’s applications.

What is Quadrature Amplitude Modulation?

Quadrature amplitude modulation (QAM) is modulation techniques that we can utilize in analog modulation concept and digital modulation concept. Depending upon the input signal form we can use it in either analog or digital modulation schemes. In QAM, we can modulate two individual signals and transmitted to the receiver level. And by using the two input signals, the channel bandwidth also increases. QAM can able to transmit two message signals over the same channel. This QAM technique also is known as “quadrature carrier multiplexing”.

Quadrature Amplitude Modulation Definition

QAM can be defined as it is s a modulation technique that is used to combine two amplitude modulated waves into a single channel to increase the channel bandwidth.

Quadrature Amplitude Modulation Block Diagram

The below diagrams show the transmitter and receiver block diagram of the QAM scheme.

QAM Modulator

qam-modulator
qam-modulator

QAM Demodulator

qam-demodulator
qam-demodulator

QAM Working Principle

“In QAM transmitter, the above section i.e., product modulator1 and local oscillator are called in-phase channel and product modulator2 and local oscillator are called a quadrature channel. Both output signals of the in-phase channel and quadrature channel are summed so the resultant output will be  QAM.”

At the receiver level, the QAM signal is forwarded from the upper channel of receiver and lower channel, and the resultant signals of product modulators are forwarded from LPF1 and LPF2. These LPF’s are fixed to the cut off frequencies of input 1 and input 2 signals. Then the filtered outputs are the recovered original signals.

The below waveforms are indicating the two different carrier signals of the QAM technique.

input-carriers-of-qam
input-carriers-of-qam

The output waveforms of QAM is shown below.

quadrature-output-signal-waveform
quadrature-output-signal-waveform

Advantages of QAM

The quadrature amplitude modulation advantages are listed below. They are

  • One of the best advantages of QAM – supports a high data rate. So, the number of bits can be carried by the carrier signal. Because of these advantages it preferable in wireless communication networks.
  • QAM’s noise immunity is very high. Due to this noise interference is very less.
  • It has a low probability of error value.
  • QAM expertly uses channel bandwidth.

Quadrature Amplitude Modulation Applications

The applications of QAM include the following.

  • The applications of QAM are mostly observed in radio communications and data delivery applications systems.
  • QAM technique has wide applications in the radio communications field because, as the increment of the data rate there is the chance of noise increment but this QAM technique is not affected by noise interference hence there is an easy mode of signal transmission can be possible with this QAM.
  • QAM has wide applications in transmitting digital signals like digital cable television and in internet services.
  • In cellular technology, wireless device technology quadrature amplitude modulation is preferred.

Thus, this is all about an overview of QAM which includes what is quadrature amplitude modulation, its definition, block diagram, working principle, and it’s applications. Here is a question for you, what are the disadvantages of QAM?

 

 

 

 



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