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.