Mumbai University > Electronics Engineering > Sem4 > Fundamentals of Communication Engineering

Marks: 5M

Year: Dec2014

1. Signal-to-noise ratio (SNR)

• Signal to noise ratio is defined as the ratio of the signal power to the noise power at the same or equivalent point in the system.
• It is a measure of signal strength relative to the background noise.
• It is often denoted as SNR and expressed in decibels.

• Signal to noise ratio is given as

  SNR = $\frac{P_S}{P_N}$ (unit: W)

  Where,

  $P_S$ = signal power,

  $P_N$= noise power.

• SNR in dB is given as:

  SNR in dB = 10 log⁡($\frac{P_S}{P_N}$ ) (unit: dBW)

2. Noise factor

• Noise factor is defined as the ratio of the SNR at the input to the SNR at the output.

• It is given as:

  F = $\frac{(\text{SNR at input})}{\text{(SNR at output)}} \\ = \frac{P_{Si}}{P_{Ni}} × \frac{P_{No}}{P_{So}}$

  • Noise factor is always greater than one, and has unity as the ideal value.

3. Noise figure

• Noise factor expressed in decibels is called as Noise figure.

• Noise figure is given as:

  Noise figure = F dB = 10 log F

  = 10 log⁡(SNR at input) - log⁡(SNR at output)

  • The ideal value of noise figure is 0 dB.

4. Equivalent noise temperature

• Equivalent noise temperature is defined as the absolute temperature at which a perfect resistor, of equal resistance to the component, would generate the same noise as the component at room temperature.

• Equivalent noise temperature given in terms of noise figure as:

  Te = $T_0$ (F-1)

  Where $T_0$ = 290K