# Modulation and Demodulation

Modulation and demodulation are the key process in communication system.Modulation is a process of varying the parameters high frequency carrier with respect to the message signal.The parameters of the carrier signal are amplitude,frequency and phase.

Demodulation is the inverse process of modulation.In demodulation we retrieve the message content from the modulated high frequency carrier.After the demodulation process the output quality may be reduced due to various parameters of channel and noise.To reduce the errors and enhance the efficiency we use various methods of modulation and demodulation.

modulation and demodulationNeed for Modulation and DemodulationAll electromagnetic waves travel at the speed of light approximately.But the sound signals which are low frequency signals and due to less energy they can not travel longer distances.We can boost the energy by modulating them using a high frequency carrier which increases the transmission efficiency.

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The antenna height is inversely proportional to the frequency of the signal.So if we use the high frequency carrier which is been modulated by the message signal the we can adopt smaller antenna heights.Demodulation which extracts the information from the modulated carrier.Types of Modulation and DemodulationThe modulation methods can be divided into two classes,analog modulation and digital modulation.In analog modulation we have amplitude modulation (AM),frequency modulation (FM),and phase modulation (PM) in which the amplitude,frequency and phase of the high frequency carrier is modified with respect to the message signal.

In digital modulation the analog data is converted into digital form using analog to digital converting techniques.In digital modulation analog high frequency carrier is modulated by digital data stream.Some of digital modulation methods:Phase-shift keying (PSK)Frequency-shift keying (FSK)Audio frequency-shift keying (AFSK)Multi-frequency shift keying (M-ary FSK or MFSK)Dual-tone multi-frequency (DTMF)Continuous-phase frequency-shift keying (CPFSK)Amplitude-shift keying (ASK)M-ary vestigial sideband modulation,Quadrature amplitude modulation (QAM) - a combination of PSK and ASK:Polar modulation like QAM a combination of PSK and ASK.Continuous phase modulation (CPM) which involves various methods.We have many demodulation methods.Popular methods are envelop detection,phase locked loop,coherent and non coherent detections and using detectors.