How to keep amplitude of PSK signal constant while doing simulation?

[pdcom]

How can we keep amplitude of PSK signal constant while doing simulation?

As we know in PSK information is in angle or phase and not in amplitude but the amplitude is fixed.
But when AWGN noise is added to modulated signal the amplitude of signal (both real and imaginary components are changed) and hence angle or phase of vector is changed and in demodulation we compare it with the orignal phase.

But how can we say that amplitude is fixed?

 

[gaffar]

Re: PSK simulation

It is not possible to fix the amplitude of a PSK modulated signal at receiver front-end in the existence of noise but you can reduce the effect of noise by increasing SNR.

 

[cheggy]

Re: PSK simulation

Well, if your (fixed) amplitude is large, noise will change it just a little, and as a result phase of your vector will change slightly and you'll be able to recognize your vector at receiving point. This is case with large signal-to-noise (SNR) ratio. In case when your fixed amplitude is small, presence of noise will change it drastically, resulting vector can be so ugly that you can't recognize it correctly at your receiver - this is low SNR case. Of course, "large" and "small" amplitudes are always considered in comparison with level of noise, that's why we always speak in terms of SNR.