Amplitude Shift Keying (ASK) Modulation

Amplitude-shift keying (ASK) is a kind of digital modulation that represents digital data as variations in the amplitude of a carrier wave.The amplitude of an analog carrier signal varies in accordance with the bit stream (modulating signal) where  frequency and phase are keeping constant. The level of amplitude can be used to represent binary logic 0s and 1s. We can think of a carrier signal as an ON or OFF switch. In the modulated signal, logic 0 is represented by the absence of a carrier, thus giving OFF/ON keying operation and hence the name given. 

Here is a diagram showing the ideal model for a transmission system using an ASK modulation:

It can be divided into three blocks. The first one represents the transmitter, the second one is a linear model of the effects of the channel, the third one shows the structure of the receiver.

What is Digital Modulation ?

In digital modulation, an analog carrier signal is modulated by a digital bit stream. The aim of digital modulation is to transfer a digital bit stream over an analog passband channel, for example over the public switched telephone network (where a bandpass filter limits the frequency range to between 300 and 3400 Hz), or over a limited radio frequency band.

Phase Modulation

In the case of PM(phase modulation) the information or AF(Audio Frequency) changes the phase of the carrier wave without changing its frequency or amplitude. Phase modulation (PM) is a form of modulation that represents information as variations in the instantaneous phase of a carrier wave.Main advantages of PM are improved signal to noise ratio and less radiated power.

The carrier signal is represented by

Frequency Modulation

In telecommunications, frequency modulation (FM) conveys information over a carrier wave by varying its frequency.In a frequency modulated system,the amplitude of the modulated carriers kept constant,while its frequency is varied in accordance with the variations of the modulating signal. . Main advantages of PM are improved signal to noise ratio and less radiated power.

Mathematically,the process can be expressed as

Amplitude modulation

Amplitude modulation(AM) is the simplest form of modulation .It is an analog-to-analog conversion method. Here the information or AF(Audio Frequency) signal changes the amplitude of the carrier wave without changing its frequency or phase. Amplitude modulation (AM) is a technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. AM works by varying the strength of the transmitted signal in relation to the information being sent.

Mathematically,the process can be expressed as

What is Analog Modulation ??

In analog modulation, the modulation is applied continuously in response to the analog information signal.The representation of analog information by an analog signal.There are two principle reasons for analog modulation of analog signals:

• ·         A higher frequency may be needed for effective transmission.

• ·         Modulation permits frequency division multiplexing.

The aim of analog modulation is to transfer an analog baseband (or lowpass) signal, for example an audio signal or TV signal, over an analog passband channel, for example a limited radio frequency band or a cable TV network channel.

            Here the main analog modulation are

• ·         Amplitude Modulation

• ·         Frequency Modulation

• ·         Phase Modulation

Modulation technique in wireless communication

 Modulation has been defined as the process of combining an input signal and a carrier signal with a specified frequency,to produce a modulated signal whose bandwidth is centered on carrier signal frequency.Modulation is the process of transforming a message signal to make it easier to work with. Modulation is the process of changing one or more properties of high frequency signal or carrier with respect to modulating signal. It usually involves varying one waveform in relation to another waveform. In telecommunications, modulation is used to convey a message, or a musician may modulate the tone from a musical instrument by varying its volume, timing and pitch. In radio communications for instance, electrical signals are best received when the transmitter and receiver are tuned to resonance. Therefore keeping the frequency content of the message signal as close as possible to the resonant frequency of the two is ideal. Often a high-frequency sinusoid waveform is used as carrier signal to convey a lower frequency signal. The three key parameters of a sine wave are its amplitude ("volume"), its phase ("timing") and its frequency ("pitch"), all of which can be modified in accordance with a low frequency information signal to obtain the modulated signal.