FSK Decoder Online (non-coherent)

Instructions for Frequency Shift Keying Modulation (FSK)

• Step 1: Click on 'Generate Message' button to generate input message signal
• Step 2: Then click on 'Generate Carrier' button to generate carrier signal
• Step 3: You can change the carrier signal frequencies from the input fields
• Step 4: Click on 'Simulate FSK' button to generate Frequency Shift Keying Signal

Carrier Frequency 1 in Hz:

Carrier Frequency 2 in Hz:

Sampling Frequency in Hz:

Bit Rate (bps):

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Frequency Shift Keying (FSK) Demodulation (non-coherent)

Mathematical Model of FSK

1. Modulation (FSK)

The transmitted signal $s(t)$ is defined piecewise based on the binary message $m(t)$:

For Bit 1 (Mark):
s(t) = A sin(2π f₁ t)

For Bit 0 (Space):
s(t) = A sin(2π f₂ t)

Where:
A = Amplitude (1)
f₁ = Carrier Frequency 1
f₂ = Carrier Frequency 2

2. Non-Coherent Demodulation

The receiver detects energy at both frequencies using Quadrature Correlation:

1. Calculate In-phase (I) and Quadrature (Q):
I = Σ [s(t) · sin(2π f t)]
Q = Σ [s(t) · cos(2π f t)]

2. Calculate Magnitude (Envelope):
M = √(I² + Q²)

The decision logic compares the magnitudes:

If M₁ > M₂, Output = 1
Else, Output = 0

Why use Magnitude (I² + Q²)?

In non-coherent detection, the receiver doesn't know the exact phase of the incoming signal. By correlating with both Sine and Cosine, we ensure that even if the signal is phase-shifted, the total energy (magnitude) will still be detected correctly.