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 حل واجب t325 spring 2017

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المساهمات : 315
تاريخ التسجيل : 18/02/2012

مُساهمةموضوع: حل واجب t325 spring 2017   السبت مارس 25, 2017 8:18 pm

T325:Technologies for digital media





___________________________________________________________________________

Tutor-marked Assignment
___________________________________________________________________________

T325: TMA, Spring2017 Cut-off date: To Be Assigned

___________________________________________________________________________
Total Marks: 100

Contents
Part 1 (50marks) ………………………………………………………………………………
Part 2 (50 marks) ………………………………………………………………………………











Plagiarism Warning:
As per AOU rules and regulations, all students are required to submit their own TMA work and avoid plagiarism. The AOU has implemented sophisticated techniques for plagiarism detection. You must provide all references in case you use and quote another person's work in your TMA. You will be penalized for any act of plagiarism as per the AOU's rules and regulations.





Part I– Impact of collaboration on battery power consumption (50 marks)

You have studied both batteries and video compression in Block 1. In Part I of the TMA, you will learn that peer-to-peer (P2P) collaboration between mobile devices to download video (or other) files can lead to battery power savings.

You are required to read the article:
[1] M. Ramadan, L. Zein and Z. Dawy, “Implementation and Evaluation of Cooperative Video Streaming for Mobile Devices,” In Proceedings of IEEE International Symposium on Personal, Indoor, and Mobile Radio Communications (PIMRC), September 2008.
It is posted on LMS, and it can be found at the link:
http://ieeexplore.ieee.org/document/4699506/

You can also (and you are encouraged to) gather information from other sources and cite them in your report.

1- What is the wireless technology used for long range (LR) communications in [1]? What is the technology used for short range (SR) communications? Can you justify this selection (why this selection was not made the other way around for example?) (5 marks)

2- Three parts can be distinguished from Fig. 4 in [1]. What can you conclude from these parts concerning the power consumption?(5 marks)

3- Looking at the three subfigures of Figure 5 in [1], what can you conclude about P2P collaboration? (Hint: how does it affect power consumption? How does it vary with the collaborating peers?)(5 marks)

4- MJPEG versus MPEG:
a. What is MJPEG? (5 marks)

b. How does it differ from MPEG?(5 marks)

c. Which one would lead to better compression? To lower energy consumption?(5 marks)

d. If MPEG is used instead of MJPEG, the value of which variable in Equation (1) would be affected? And why?(5 marks)

5- Numerical Example:
a. In the case of no collaboration (N=1), how would equation (1) in paper [1] become? (5 marks)

b. The definition of each parameter is given in Table II in [1]. In the table below, a numerical example is considered:



Parameter Value
RL 720 kbits/s
RS 221 kbits/s
F 30 frames/s
S 20000 bits/frame (on average)
N Different values will be considered
PL,Rx 0.5
PS,Rx 0.014
PS,Tx 0.015
Pprocessing 0.188 W
Pidle 0.95


Implement Equation (1) of [1] with the parameters from the Table above and:(10 marks)
i. N=1 (No collaboration)
ii. N=2 (Collaboration between 2 peers)
iii. N=3 (Collaboration between 3 peers)
iv. N=4 (Collaboration between 4 peers)
v. N=5 (Collaboration between 5 peers)

Part II - Steganography (50 marks)

In Block 2 of T325, you learned briefly about steganography during the discussion of watermarking. In this part of the TMA, you will learn more about steganography. Read the article: “Hide and Seek: An Introduction to Steganography”. It is posted on LMS, and it can be found at the link:http://niels.xtdnet.nl/papers/practical.pdf
You can also (and you are encouraged to) gather information from other sources and cite them in your report.
1. Provide a description of steganography and its usage. (10 marks)

2. From the document you read, give one example of how steganography can be used. (5 marks)

3. You will now consider a very simple example showing the use of steganography:
a. An army General embeds a secret message to the commander of a division of his troops in a file containing a fully white image. In this file, each pixel is encoded as a 1-byte (8 bits) integer, as shown in Table 1. In this kind of file, a black pixel would correspond to a value of 0 (a byte with all 0’s) and a white pixel would correspond to a value of 255 (a byte with all 1’s). All other intermediate values correspond to different shades of grey.
Table 1: Binary data from white image file
11111111 11111111 11111111 11111111 11111111 11111111 11111111 11111111
11111111 11111111 11111111 11111111 11111111 11111111 11111111 11111111
11111111 11111111 11111111 11111111 11111111 11111111 11111111 11111111
11111111 11111111 11111111 11111111 11111111 11111111 11111111 11111111
11111111 11111111 11111111 11111111 11111111 11111111 11111111 11111111
11111111 11111111 11111111 11111111 11111111 11111111 11111111 11111111
11111111 11111111 11111111 11111111 11111111 11111111 11111111 11111111
11111111 11111111 11111111 11111111 11111111 11111111 11111111 11111111
11111111 11111111 11111111 11111111 11111111 11111111 11111111 11111111
11111111 11111111 11111111 11111111 11111111 11111111 11111111 11111111
11111111 11111111 11111111 11111111 11111111 11111111 11111111 11111111
11111111 11111111 11111111 11111111 11111111 11111111 11111111 11111111
11111111 11111111 11111111 11111111 11111111 11111111 11111111 11111111
11111111 11111111 11111111 11111111 11111111 11111111 11111111 11111111
11111111 11111111 11111111 11111111 11111111 11111111 11111111 11111111
The General modifies the file of Table 1 so that it becomes as shown in Table 2.
Table2: Binary data from modified white image file after embedding a steganographic message.
11111110 11111111 11111110 11111110 11111110 11111110 11111110 11111111
11111110 11111111 11111111 11111111 11111110 11111111 11111110 11111110
11111110 11111111 11111111 11111111 11111110 11111111 11111110 11111110
11111110 11111111 11111111 11111110 11111110 11111110 11111110 11111111
11111110 11111111 11111111 11111110 11111110 11111110 11111111 11111111
11111110 11111111 11111111 11111110 11111111 11111110 11111111 11111111
11111110 11111110 11111111 11111110 11111110 11111110 11111110 11111110
11111110 11111111 11111111 11111110 11111110 11111110 11111110 11111111
11111110 11111111 11111111 11111111 11111110 11111111 11111110 11111110
11111110 11111110 11111111 11111110 11111110 11111110 11111110 11111110
11111110 11111111 11111111 11111110 11111110 11111111 11111110 11111110
11111110 11111111 11111111 11111110 11111110 11111110 11111110 11111111
11111110 11111111 11111111 11111111 11111110 11111111 11111111 11111111
11111110 11111111 11111111 11111110 11111111 11111111 11111111 11111110
11111110 11111110 11111111 11111110 11111111 11111111 11111111 11111110
Try to check for concealed information in the file by looking at the least significant bits (LSBs) of each byte:
i. Group the LSBs of the bytes in each row into a single byte. (7.5 marks)
ii. Try to treat the byte obtained from each row as the ASCII code of a character and try to determine the letter or character corresponding to each row. Use the provided ASCII table (Table 3) to do the mapping. (7.5 marks)
iii. Group the decoded characters to try to obtain a meaningful message. What is the result? What can you conclude? (5 marks)



b. Now you will discover why the LSB, and not any other bit, is used for steganography:
i. If the LSB changes from 1 to 0, what does the new numerical value of a pixel in Table 1 become? What is the percentage of error compared to the initial value?(4 marks)
ii. Assume now that, instead of the LSB, the most significant bit (MSB) is selected to be used for steganography. If the MSB changes from 1 to 0, what does the new numerical value of the pixel become? What is the percentage of error compared to the initial value?(4 marks)
iii. Can you now conclude whey the LSB is used? Explain(2 marks)
Table 3. ASCII codes in binary
Letter Binary Letter Binary
a 01100001 A 01000001
b 01100010 B 01000010
c 01100011 C 01000011
d 01100100 D 01000100
e 01100101 E 01000101
f 01100110 F 01000110
g 01100111 G 01000111
h 01101000 H 01001000
i 01101001 I 01001001
j 01101010 J 01001010
k 01101011 K 01001011
l 01101100 L 01001100
m 01101101 M 01001101
n 01101110 N 01001110
o 01101111 O 01001111
p 01110000 P 01010000
q 01110001 Q 01010001
r 01110010 R 01010010
s 01110011 S 01010011
t 01110100 T 01010100
u 01110101 U 01010101
v 01110110 V 01010110
w 01110111 W 01010111
x 01111000 X 01011000
y 01111001 Y 01011001
z 01111010 Z 01011010
[SPACE] 00100000 . [period] 00101110
4. The method described in Part II could also be used to embed a watermark in a certain digital document (although it is a simple, not very robust method). However, you learned in Block 2 that watermarking is not quite the same as steganography. Explain. (5 marks)

_________________
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