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## Advantages of MFSK | Disadvantages of MFSK | Multiple Frequency Shift Keying

Introduction: M-FSK (M-array FSK) is variant of binary FSK which uses two tones. Following equations are used to map binary data in FSK (Frequency Shift Keying).
s(t) = A* cos(2*π*f1*t) for Binary 1
s(t) = A* cos(2*π*f2*t) for Binary 0
Here 'f1' and 'f2' are offset from center frequency used in the system.
The figure depicts FSK modulation waveforms for binary 1 and binary 0 data. There are different M-ary modulation techniques viz. M-ary PSK, M-ary QAM and M-ary FSK. In these modulation techniques, digital data is sent by varying envelope and phase or frequency of an RF carrier. As these techniques map baseband digital data on four or more RF carriers and hence it is called M-ary modulation.

### What is M-FSK?

MFSK uses multiple frequency tones to map digital data before transmission. It uses narrow tone spacing so that higher data rates can be achieved with given bandwidth. The generalised equation for MFSK can be expressed as follows.
➨ Xi(t) = A* cos (2*π*fi*t)
Where,
fi = fc + (2*i - 1 - M)*fd
Where,
fi is frequency of ith signal
fc is center frequency
fd is frequency deviation
M is Modulation order or number of possible signals (M = 2 for BPSK, M = 4 for QPSK etc.)
Number of bits/symbol, K = log2(M)

For example in 4FSK with fc of 250 KHz and fd of 25 KHz, we will get 2 bits per symbol as M is 4. The four frequencies used to map binary data (00, 01, 10, 11) are 175 KHz, 225 KHz, 275 KHz and 325 KHz.

The typical applications of M-FSK include VHF/UHF communication, telephone signaling (i.e. DTMF), Digital Mobile Radio (DMR), bluetooth (i.e. FHSS) etc. Refer 2FSK and 4FSK Modulation types >>.

### Benefits or advantages of MFSK

It overcomes drawbacks of BFSK (Binary FSK or 2FSK) modulation scheme. Following are the benefits or advantages of MFSK:
➨Error rate is less due to increased frequency tones.
➨It is tolerant to ionospheric channel effects such as doppler, multi-path and fading.
➨It is more robust compare to PSK modulation scheme.

### Drawbacks or disadvantages of MFSK

Following are the drawbacks or disadvantages of MFSK:
➨Tuning at receiver is complex due to narrow bandwith and narrow spacing of individual tone detectors.
➨It is essential to have lower Tx/Rx offset and good stability of transceiver module.
➨MFSK utilizes more bandwidth compare to PSK modulation for same text speed.