Thursday, May 19, 2011

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.
The following notation is used:
  • ·         ht(t) is the carrier signal for the transmission
  • ·         hc(t) is the impulse response of the channel
  • ·         n(t) is the noise introduced by the channel
  • ·         hr(t) is the filter at the receiver
  • ·         L is the number of levels that are used for transmission
  • ·         Ts is the time between the generation of two symbols.
Now we will discuss about advantages of ASK and disadvantages of  ASK.
Advantages of Amplitude-shift keying (ASK): The main advantage of ASK modulation is  generation of ASK is very much easy. Both ASK modulation and demodulation processes are relatively inexpensive. The ASK technique is also commonly used to transmit digital data over optical fiber. There are many other advantages of  ASK, Such as Amplitude-shift keying transmitters are very simple and transmitter current is lower than FSK. One important advantage of ASK is it need lees bandwidth than FSK. 

Disadvantages of Amplitude-shift keying (ASK): Unfortunately, ASK is linear and sensitive to atmospheric noise, distortion, propagation condition on different routes in PSTN.It requires excessive bandwidth and is therefore a waste of power.

2 comments:

  1. advantage -ASK ,it need lees bandwidth than FSK.
    disadvantage-It requires excessive bandwidth and is therefore a waste of power.
    HOW IT IS POSSIBLE

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