The short form of Frequency Shift Keying is known as FSK. It is also a digital modulation technique. In this technique, the frequency of the RF carrier varies depending on the digital baseband input. The figure shows the FSK modulation. As shown, binaries 1 and 0 are represented by two different carrier frequencies. The figure shows that binary 1 is represented by the high frequency 'f1' and binary 0 is represented by the low frequency 'f2'.
Fig.2 FSK
The binary FSK can be represented by the following equation:
s (t) = A * cos (2 * π * f1 * t) for Binary 1
s (t) = A * cos (2 * π * f2 * t) for Binary 0
In FSK modulation, the NRZ signaling method is used. The bandwidth requirement in the case of FSK is:
BW = 2 * Rb + (f1-f2)
• In the case of FSK, Pe is smaller and SNR is high.
• This technique is widely used in the design and development of modems.
• Increased noise immunity, but requires a higher bandwidth compared to other types of modulation.
ASK
The short form of Amplitude Shift Keying is known as ASK. It is the technique of digital modulation. In this technique, the amplitude of the RF carrier varies according to the digital baseband input signal. The figure represents the operation of the ASK modulation. As shown in the figure, the binary 1 will be represented by a carrier signal with some amplitude while the binary 0 will be represented by a carrier of zero amplitude (ie, without carrier).
Fig.1 ASK Modulation
The ASK modulation can be represented by the following equation:
s (t) = A2 * cos (2 * π * fc * t) for Binary Logic-1
s (t) = A1 * cos (2 * π * fc * t) for Binary Logic-0
Here A2> A1
The signaling used is ON-OFF signaling.
The bandwidth requirement for ASK is:
BW = 2 / Tb = 2 * Rb
Often in ASK modulation, binary-1 is represented by the carrier with amplitude-A2 and binary-0 is represented by the carrier with amplitude-A1. Here A2 is greater in magnitude than A1. The ASK form in which no carrier is transmitted during the logical zero transmission is known as OOK (On Off Key Modulation) modulation. This is shown in figure-1. See the OOK vs. ASK modulation >> that compares OOK vs ASK and shows the difference between the OOK and ASK modulation types with signal diagrams.
• In ASK the error probability (Pe) is high and SNR is lower.
• Has the least immunity to noise from noise.
• ASK is an efficient system of bandwidth but has less energy efficiency.