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Consider a baseband binary PAM receiver shown below. The additive channel noise $n(t)$ is white with power spectral density $S_{N}(f)=N_{0} / 2=10^{-20}$ W/Hz. The low-pass filter is ideal with unity gain and cutoff frequency $1 \; \mathrm{MHz}$. Let $Y_{t}$ represent the random variable $y\left(f_{t}\right)$.
$\begin{array}{ll} Y_{t}=N_{k} & \text { if transmitted bit } b_{k}=0 \\ Y_{t}=a+N_{k} & \text { if transmitted bit } b_{k}=1 \end{array}$
where $N_{k}$ represents the noise sample value. The noise sample has a probability density function. $P_{N_{1}}(n)=0.5 \alpha c^{\cdot \epsilon \text { d.d }}$ (This has mean zero and variance $2 / \alpha^{2}$ ). Assume transmitted bits to be equiprobable and threshold $z$ is set lo a/2 $=10^{-6} \mathrm{~V}$.
The value of the parameter $\alpha$ (in $V^{-1}$ ) is
1. $10^{10}$
2. $10^{}$
3. $1.414 \times 10^{-10}$
4. $2 \times 10^{20}$