# Engineering Question

*label*Engineering

*timer*Asked: Nov 14th, 2016

**Question description**

Hi, I have difficulty starting with communication theory. I understand the source signal u(t) goes through a transmitter and amplified by a factor then we get s(t). After it passes the channel a white noise is added to it with certain power density r(t)=s(t)+n. At receiver side we scale down this signal in order to minimize the noise n, v(t) = a · r(t).

But I have no idea how to choose this scale down factor a. I understand that if you amplify it as much as possible at transmitter side then scale it down to original size most of the noise will be reduced. For example s(t) = a · u(t), then at receiver side v(t) = 1/a * r(t), thus the 2 a will be canceled.

But from the question and answer I have it seems different, I have no idea how that optimal alpha factor is calculated.