meaning of "Input signal power" in AWGN block

Hi,

the AWGN block has a parameter called "Input signal power". How can the power be measured if the input is just an integer number? Can anyone give an example?

Thanks Senmeis

Answer 1

[Sourabh]

Hey @Owen

The “Input signal power” parameter is used by the “AWGN Channel” block to determine the amount of noise to add, especially when you specify noise in terms of “Eb/No” (energy per bit to noise power spectral density ratio) or “SNR” (signal-to-noise ratio).

Power is basically the “mean squared value” of the signal (assuming zero mean).

In recent releases of MATLAB, the Simulink AWGN Channel block has a parameter named “Input signal power, referenced to 1 ohm (watts)”.

Using the formula power = (voltage² / resistance), and resistance fixed to 1 ohm, the power is calculated as

Examples:

• Input: A constant integer (e.g., all 1s),
• Then, Power = 1² = 1 watt
• Input: Alternating between +1 and -1 (BPSK),
• Then, Power = (1² + (-1)²)/2 = 1 watt
• Input: Range from 0 to 3 (like symbol levels in 4-PAM),
• Then, Power = mean([0², 1², 2², 3²]) = (0+1+4+9)/4 = 3.5 watts

For more information, kindly refer the following MATLAB documentation resources:

• https://www.mathworks.com/help/comm/ref/awgnchannel.html
• https://www.mathworks.com/help/comm/ug/awgn-channel.html
• https://www.mathworks.com/help/simrf/ug/power-in-simulink-sources-and-signals.html

I hope this helps!