Modulation Essay

2983 words - 12 pages

Modulation is the process of encoding information from a message source in a manner suitable for transmission.It involves translating a baseband message signal to a bandpass signal at frequencies that are very high compared to the baseband frequency. Baseband signal is called modulating signal.Bandpass signal is called modulated signal.

In telecommunications, modulation is the process of conveying a message signal, for example a digital bit stream or an analog audio signal, inside another signal that can be physically transmitted. Modulation of a sine waveform transforms a baseband message signal into a passband signal.

A modulator is a device that performs ...view middle of the document...

❑ AM carrier signal has time-varying envelope.

■ The amplitude of high-carrier signal is varied according to the instantaneous amplitude of the modulating message signal m(t).

■ Amplitude modulation (AM) is a modulation technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. AM works by varying the strength (amplitude) of the carrier in proportion to the waveform being sent. That waveform may, for instance, correspond to the sounds to be reproduced by a loudspeaker, or the light intensity of television pixels. This contrasts with frequency modulation, in which the frequency of the carrier signal is varied, and phase modulation, in which its phase is varied, by the modulating signal.

■ AM was the earliest modulation method used to transmit voice by radio. It was developed during the first two decades of the 20th century beginning withReginald Fessenden's radiotelephone experiments in 1900. It remains in use today in many forms of communication; for example it is used in portable two way radios, VHF aircraft radio and in computer modems.[citation needed] "AM" is often used to refer to mediumwave AM radio broadcasting.


Frequency modulation

Most popular analog modulation technique

Amplitude of the carrier signal is kept constant (constant envelope signal), the frequency of carrier is changed according to the amplitude of the modulating message signal; Hence info is carried in the phase or frequency of the carrier. In telecommunications and signal processing, frequency modulation (FM) is the encoding of information in a carrier wave by varying the instantaneous frequency of the wave. (Compare with amplitude modulation, in which the amplitude of the carrier wave varies, while the frequency remains constant.)

Has better noise immunity:

• atmospheric or impulse noise cause rapid fluctuations in the amplitude of the received signal

• Performs better in multipath environment

• Small-scale fading cause amplitude fluctuations as we have seen earlier.

• Can trade bandwidth occupancy for improved noise performance.

• Increasing the bandwith occupied increases the SNR ratio.

• The relationship between received power and quality is non-linear.

• Rapid increase in quality for an increase in received power.

• Resistant to co-channel interference (capture effect).


• Digital modulation
• Linear modulation techniques



1. Generation of BPSK modulated signal and demodulation of the same after passing through the channel.

2. Compare the demodulation schemes using:

     (a) Squaring loop.  

     (b) Costa’s loop.

3. Observe the spectrum of BPSK Signal and effect of variation of channel bandwidth

4. Determine the error rates.



IIn phase shift keying...

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