power of sinusoid signal

I am reading an article about ADC. This part is confusing.
If the analog input is a sinusoid with amplitude Vref/2 (peak-to-peak Vref), its total power is equal to Vref/ 8.

P = U^2/R = (Vref/2√2)^2 /R = Vref/(8R)
Why is R omitted here? I mean that why R = 1.

 

I'm assuming it's because SNR is the ratio of two powers.
Psig=Vsig^2/R
Pnoise=Vnoise^2/R
Psig/Pnoise=((Vsig^2)/R)/((Vnoise^2)/R)
Psig/Pnoise=Vsig^2/Vnoise^2

The R cancels out, so it is irrelevant.

 

Thanks, that makes sense!
I want to ask one more question.
SNRp means "peak signal to noise ratio". Why we need to include "p" here?
Because this is a ratio between two signals, the ratio doesn't depend on if is peak or root mean square?