9.4 COMPARISON OF DIFFERENT MODULATION TECHNIQUES

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Before we discuss the details of different modulation techniques, it is important to understand why so many modulation schemes are available. The reason for having different modulation schemes is that the performance of each modulation scheme is different. The performance criteria on which modulation techniques can be compared are:

Bandwidth: What is the bandwidth of the modulated wave?

Noise immunity: Even if noise is added to the modulated signal on the transmission medium, can the original modulating signal be obtained by the demodulator without much distortion?

Complexity: What is the complexity involved in implementing the modulator and demodulator? Generally, the modulator and demodulator are implemented as hardware, though nowdays, digital signal processors are used for implementation, and hence a lot of software is also used.

The performance of a modulation scheme can be characterized by the bandwidth of the modulated signal, immunity to noise and the complexity of the modulator/demodulator hardware.

Based on these performance criteria, a modulation technique has to be chosen for a given application.

Note

In the past, both modulator and demodulator were implemented completely in hardware. With the advent of digital signal processors, modulator and demodulator implementations are now software oriented.

Note

How well a modulation scheme performs on a noisy channel is characterized by the Bit Error Rate (BER). The BER is related to the signal-to-noise ratio (SNR). For a given BER, say 10⁻³, the modulation technique that requires the least SNR is the best.

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