# Quadrature Amplitude Modulation : Working Principle and Its Applications

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”.

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 Working Principle

“In the QAM transmitter, the above section i.e., product modulator1 and local oscillator are called the 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.

The output waveforms of QAM is shown below.

• 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.