Line 7: Line 7:
 
----
 
----
  
&nbsp;<font color="#ff0000"><span style="font-size: 19px;"><math>\color{blue}\text{1. } \left( \text{25 pts} \right) \text{ Let X, Y, and Z be three jointly distributed random variables with joint pdf} f_{XYZ}\left ( x,y,z \right )= \frac{3z^{2}}{7\sqrt[]{2\pi}}e^{-zy} exp \left [ -\frac{1}{2}\left ( \frac{x-y}{z}\right )^{2} \right ] \cdot 1_{\left[0,\infty \right )}\left(y \right )\cdot1_{\left[1,2 \right]} \left ( z \right) </math></span></font>  
+
&nbsp;<font color="#ff0000"><span style="font-size: 19px;"><math>\color{blue}\text{Consider the following discrete space system with input } x(m,n) \text{ and output } y(m,n).
 +
</math></span></font>  
  
'''<math>\color{blue}\left( \text{a} \right) \text{ Find the joint probability density function } f_{YZ}(y,z).</math>'''<br>  
+
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; <math>\color{blue}
 +
y(m,n) = \sum_{k=-\infty}^{\infty}{\sum_{l=-\infty}^{\infty}{x(m-k,n-l)h(k,l)}}.
 +
</math><br>  
  
===== <math>\color{blue}\text{Solution 1:}</math>  =====
 
  
<math> f_{YZ}\left (y,z \right )=\int_{-\infty}^{+\infty}f_{XYZ}\left(x,y,z \right )dx </math>&nbsp;
+
<math>\color{blue}
 +
\text{For parts a) and b) let}
 +
</math><br>
 +
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; <math>\color{blue}
 +
h(m,n)=sinc(mT,nT)
 +
</math><br>
 +
<math>\color{blue}  
 +
\text{where } T\leq1.
 +
</math><br>
  
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;<math> =\frac{3z^{2}}{7\sqrt[]{2\pi}}e^{-zy}\int_{-\infty}^{+\infty}exp\left[-\frac{1}{2}\left(\frac{x-y}{z} \right )^{2} \right ]dx\cdot 1_{[0,\infty)}
 
\left(y \right )\cdot1_{\left [1,2 \right ]}\left(z \right )</math><br>
 
  
<math>\text{But}\int_{-\infty}^{+\infty}exp\left[-\frac{1}{2}\left(\frac{x-y}{z} \right )^{2} \right ]dx \text{looks like the Gaussian pdf, so} </math>  
+
<math>\color{blue}
 +
\text{For parts c), d), and e) let}
 +
</math><br>
 +
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; <math>\color{blue}
 +
h(m,n)=sinc\left( \frac{(n+m)T}{\sqrt[]{2}},\frac{(n-m)T}{\sqrt[]{2}} \right)
 +
</math><br>
 +
<math>\color{blue}
 +
\text{where } T\leq1.
 +
</math><br>
  
<math> =\frac{3z^{2}}{7\sqrt[]{2\pi}}e^{-zy}
+
 
\underset{\sqrt[]{2\pi}z}{\underbrace{\frac{7\sqrt[]{2\pi}z}{7\sqrt[]{2\pi}z}  \int_{-\infty}^{+\infty}exp\left[-\frac{1}{2}\left(\frac{x-y}{z} \right )^{2} \right ]dx}}\cdot 1_{[0,\infty)}
+
 
\left(y \right )\cdot1_{\left [1,2 \right ]}\left(z \right )
+
<math>\color{blue}\text{a) Calculate the frequency response, }H \left( e^{j\mu},e^{j\nu} \right).</math><br>
</math>
+
 
 +
===== <math>\color{blue}\text{Solution 1:}</math> =====
  
 
<math>
 
<math>
=\frac{3z^{2}}{7}e^{-zy}\cdot 1_{[0,\infty)}
+
 
\left(y \right )\cdot1_{\left [1,2 \right ]}\left(z \right )
+
 
 
</math>
 
</math>
  
Line 37: Line 54:
 
----
 
----
  
<math>\color{blue}\left( \text{b} \right) \text{Find}  
+
<math>\color{blue}\text{b) Sketch the frequency response for } |\mu| < 2\pi \text{ and } |nu| < 2\pi \text{ when } T = \frac{1}{2}
f_{x}\left( x|y,z\right )
+
 
</math><br>  
 
</math><br>  
  
Line 44: Line 60:
  
 
<font color="#ff0000"><span style="font-size: 17px;">'''<font face="serif"></font><math>
 
<font color="#ff0000"><span style="font-size: 17px;">'''<font face="serif"></font><math>
= \frac{f_{XYZ}\left( x,y,z\right )}{f_{YZ}\left(y,z \right )}
+
 
 +
 
 
</math>'''</span></font><font color="#ff0000"><span style="font-size: 17px;">
 
</math>'''</span></font><font color="#ff0000"><span style="font-size: 17px;">
 
</span></font>  
 
</span></font>  
  
'''<font face="serif"><math>
 
= \frac{e^{-\frac{1}{2}\left(\frac{x-y}{z} \right )^{2}}}{\sqrt[]{2\pi}z}
 
</math>&nbsp;&nbsp;</font>'''
 
  
 
----
 
----
Line 57: Line 71:
  
 
sol2 here
 
sol2 here
 +
 
----
 
----
  
<math>\color{blue}\left( \text{c} \right) \text{Find}  
+
<math>\color{blue}\text{c) Calculate the frequency response, }H \left( e^{j\mu},e^{j\nu} \right).</math><br>  
f_{Z}\left( z\right )
+
</math><br>  
+
  
 
<math>\color{blue}\text{Solution 1:}</math>  
 
<math>\color{blue}\text{Solution 1:}</math>  
  
 
<font color="#ff0000"><span style="font-size: 17px;">'''<font face="serif"></font><math>
 
<font color="#ff0000"><span style="font-size: 17px;">'''<font face="serif"></font><math>
=\int_{0}^{+\infty}{f_{YZ}\left(y,z \right )dy}
+
 
 
</math>'''</span></font><font color="#ff0000"><span style="font-size: 17px;">
 
</math>'''</span></font><font color="#ff0000"><span style="font-size: 17px;">
 
</span></font>  
 
</span></font>  
  
 
'''<font face="serif"><math>
 
'''<font face="serif"><math>
=\frac{3z^{2}}{7}\cdot1_{\left[1,2 \right ]}(z)
+
 
 
</math>&nbsp;&nbsp;</font>'''  
 
</math>&nbsp;&nbsp;</font>'''  
  
Line 81: Line 94:
 
----
 
----
  
<math>\color{blue}\left( \text{d} \right) \text{Find}  
+
<math>\color{blue}\text{d) Sketch the frequency response for } |\mu| < 2\pi \text{ and } |nu| < 2\pi \text{ when } T = \frac{1}{2}
f_{Y}\left(y|z \right )
+
 
</math><br>  
 
</math><br>  
  
Line 88: Line 100:
  
 
<font color="#ff0000"><span style="font-size: 17px;">'''<font face="serif"></font><math>
 
<font color="#ff0000"><span style="font-size: 17px;">'''<font face="serif"></font><math>
=\frac{f_{YZ}\left(y,z \right )}{f_{Z}(z)}</math>'''</span></font><font color="#ff0000"><span style="font-size: 17px;">
+
 
 +
</math>'''</span></font><font color="#ff0000"><span style="font-size: 17px;">
 
</span></font>  
 
</span></font>  
 
'''<font face="serif"><math>
 
=e^{-zy}z\cdot1_{\left[0,\infty \right )}(y)
 
</math>&nbsp;&nbsp;</font>'''
 
  
 
----
 
----
Line 101: Line 110:
 
sol2 here
 
sol2 here
 
----
 
----
<math>\color{blue}\left( \text{e} \right) \text{Find}  
+
<math>\color{blue}\text{e) Calculate } y(m,n) \text{ when } x(m,n)=1.</math><br>
f_{XY}\left(x,y|z \right )
+
 
</math><br>  
+
  
 
<math>\color{blue}\text{Solution 1:}</math>  
 
<math>\color{blue}\text{Solution 1:}</math>  
  
 
<font color="#ff0000"><span style="font-size: 17px;">'''<font face="serif"></font><math>
 
<font color="#ff0000"><span style="font-size: 17px;">'''<font face="serif"></font><math>
=\frac{f_{XYZ}\left(x,y,z \right )}{f_{Z}(z)}
+
 
 
</math>'''</span></font><font color="#ff0000"><span style="font-size: 17px;">
 
</math>'''</span></font><font color="#ff0000"><span style="font-size: 17px;">
 
</span></font>  
 
</span></font>  
 
'''<font face="serif"><math>
 
=\frac{e^{-zy}}{\sqrt[]{2\pi}}e^{-\frac{1}{2}\left(\frac{x-y}{z} \right )^{2}}\cdot1_{\left[0,\infty \right )}(y)
 
</math>&nbsp;&nbsp;</font>'''
 
  
 
----
 
----

Revision as of 18:03, 30 July 2012

ECE Ph.D. Qualifying Exam in "Communication, Networks, Signal, and Image Processing" (CS)

Question 5, August 2011, Part 1

Part 1,2]

 $ \color{blue}\text{Consider the following discrete space system with input } x(m,n) \text{ and output } y(m,n). $

                $ \color{blue} y(m,n) = \sum_{k=-\infty}^{\infty}{\sum_{l=-\infty}^{\infty}{x(m-k,n-l)h(k,l)}}. $


$ \color{blue} \text{For parts a) and b) let} $
                $ \color{blue} h(m,n)=sinc(mT,nT) $
$ \color{blue} \text{where } T\leq1. $


$ \color{blue} \text{For parts c), d), and e) let} $
                $ \color{blue} h(m,n)=sinc\left( \frac{(n+m)T}{\sqrt[]{2}},\frac{(n-m)T}{\sqrt[]{2}} \right) $
$ \color{blue} \text{where } T\leq1. $


$ \color{blue}\text{a) Calculate the frequency response, }H \left( e^{j\mu},e^{j\nu} \right). $

$ \color{blue}\text{Solution 1:} $



$ \color{blue}\text{Solution 2:} $

here put sol.2


$ \color{blue}\text{b) Sketch the frequency response for } |\mu| < 2\pi \text{ and } |nu| < 2\pi \text{ when } T = \frac{1}{2} $

$ \color{blue}\text{Solution 1:} $



$ \color{blue}\text{Solution 2:} $

sol2 here


$ \color{blue}\text{c) Calculate the frequency response, }H \left( e^{j\mu},e^{j\nu} \right). $

$ \color{blue}\text{Solution 1:} $

  


$ \color{blue}\text{Solution 2:} $

sol2 here


$ \color{blue}\text{d) Sketch the frequency response for } |\mu| < 2\pi \text{ and } |nu| < 2\pi \text{ when } T = \frac{1}{2} $

$ \color{blue}\text{Solution 1:} $


$ \color{blue}\text{Solution 2:} $

sol2 here


$ \color{blue}\text{e) Calculate } y(m,n) \text{ when } x(m,n)=1. $


$ \color{blue}\text{Solution 1:} $


$ \color{blue}\text{Solution 2:} $

sol2 here


"Communication, Networks, Signal, and Image Processing" (CS)- Question 5, August 2011

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