# RF Wireless World

## ASK vs FSK vs PSK | Difference between ASK, FSK, PSK modulation

This page on ASK vs FSK vs PSK provides difference between ASK, FSK, PSK modulation types. All these are digital modulation techniques. Unlike Analog modulation, here input is in digital binary form. The other input is the RF carrier. Input binary data is referred as modulating signal and output is referred as modulated signal.

The short form of Amplitude Shift Keying is referred as ASK. It is the digital modulation technique. In this technique, amplitude of the RF carrier is varied in accordance with baseband digital input signal. The figure depicts operation of ASK modulation. As shown in the figure, binary 1 will be represented by carrier signal with some amplitude while binary 0 will be represented by carrier of zero amplitude(i.e. no carrier). ASK modulation can be represented by 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

Signalling used is ON-OFF signalling.
BW = 2/Tb = 2*Rb

Often in ASK modulation, binary-1 is represented by carrier with amplitude-A2 and binary-0 is represented by carrier with amplitude-A1. Here A2 is greater in magnitude compare to A1. The form of ASK where in no carrier is transmitted during the transmission of logic zero is known as OOK modulation (On Off Keying modulation). This is shown in the figure-1. Refer OOK vs ASK modulation >> which compares OOK vs ASK and depicts difference between OOK and ASK modulation types with signal diagrams.

• In ASK probability of error (Pe) is high and SNR is less.
• It has lowest noise immunity against noise.
• ASK is a bandwidth efficient system but it has lower power efficiency.

### FSK

The short form of Frequency Shift Keying is referred as FSK. It is also digital modulation technique. In this technique, frequency of the RF carrier is varied in accodance with baseband digital input. The figure depicts the FSK modulation. As shown, binary 1 and 0 is represented by two different carrier frequencies. Figure depicts that binary 1 is represented by high frequency 'f1' and binary 0 is represented by low frequency 'f2'. Fig.2 FSK

Binary FSK can be represented by 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, NRZ signalling method is used. Bandwidth requirement in case of FSK is:
BW = 2*Rb + (f1-f2)

• In case of FSK, Pe is less and SNR is high.
• This technique is widely employed in modem design and development.
• It has increased immunity to noise but requires larger bandwidth compare to other modulation types.

In order to overcome drawbacks of BFSK (Two level Binary FSK) , multiple FSK modulation techniques with more than two frequencies have been developed. In MFSK (Multiple FSK), more than one bits are represented by each signal elements.
Refer 2FSK and 4FSK Modulation types>>.

### PSK

The short form of Phase Shift Keying is referred as PSK. It is digital modulation technique where in phase of the RF carrier is changed based on digital input. Figure depicts Binary Phase Shift Keying modulation type of PSK. As shown in the figure, Binary 1 is represented by 180 degree phase of the carrier and binary 0 is represented by 0 degree phase of the RF carrier. Fig.3 PSK

Binary PSK can be represented by following equation :
If s(t) = A*cos(2*π*fc*t) for Binary 1 than
s(t) = A*cos(2*π*fc*t + π) for Binary 0

In PSK modulation, NRZ signalling is used. Bandwidth requirement for PSK is:
BW = 2 * Rb = 2 * Bit rate

• In case of PSK probability of error is less. SNR is high.
• It is a power efficient system but it has lower bandwidth efficiency.
• PSK modulation is widely used in wireless transmission.
• The variants of basic PSK and ASK modulations are QAM, 16-QAM, 64-QAM and so on.

### Modulation types

BPSK -This page describes BPSK modulation technique with equation and constellation diagram.
QPSK -This page describes QPSK modulation technique with equation and constellation diagram.