Faculty of Computer Studies
T325
Technologies For Digital Media
Mid-term Examination – Makeup – Answer Key
Second Semester
Date:
Number of Exam Pages:
(including this cover sheet(
(7)
Time Allowed: 2 Hours
Instructions:
1. Write the answers on the separate answer booklet
2. Total marks: 100 marks
3. The exam consists of three parts:
A. Multiple choice part (10 marks): You should answer All 10 questions
B. Short questions part (36 marks): You should answer 6 questions out of 10
C. Long questions/Exercises part (54 marks): You should answer all 5 questions
4. The use of calculators is allowed
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Part I: Multiple Choice questions (10 marks)
This part consists of 10 questions carrying a WEIGHT OF 1 mark each. You must answer
ALL of the following Multiple-choice questions. You should dedicate approximately 20
minutes for this part
1- Which of the following is true concerning power consumption?
a. Power consumption is one of the main constraints on the design of electronic goods
b. Power consumption is a major consideration for mobile devices and even for mainspower equipment
c. Most of the power consumed ends up as heat.
d. All of the above
2- Battery self-discharge can be defined as follows:
a. Battery loses charge even when not in use
b. Time taken by a battery to reach its maximum charge
c. Time taken by the battery to loose its charge
d. Length of time a battery can be stored even if it is not being used
3- Which of the following can be considered as an advantage of magnetic disks compared with
other memory technologies
a. Cheaper
b. Higher capacity
c. Faster access times
d. All of the above
4- Which of the following is True for a non-volatile medium
a. Patterns persist unless they are removed or changed
b. Does not depend on a continual supply of power
c. A typical example of this category is the Read Only Memory
d. All of the above are correct
5- A Reed-Solomon code represented as (n, k ) can correct up to
a. (n – k) symbol errors
b. (n – k) erasures
c. (n – k)/2 erasures
d. 2 * (n – k) symbol errors
6- Errors were occurred in two bits when 200 bits were transmitted through a channel. The bit
error ratio of the channel is
a. 0.01
b. 0.1
c. 1
d. 100
7- The range of colors available on a display or a printer is called its _______
a. Pixel
b. Gamut
c. Chromaticity
d. Luminance
8- ______________ is a common representation of a 3D object is through a set of points, or
vertices joined by straight lines.
a. Rendering
b. Wireframe
c. Frame
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d. Virtualization
9- In MPEG, part of the audio coding relies on a perception phenomenon known as
a. Noise masking
b. Frequency division
c. Temporal compression
d. Signal masking
10- Which of the following is TRUE when comparing digital and analog techniques
a. Digital techniques allow much greater processing flexibility than analogue
b. Digital material can be re-recorded many times over without loss of quality.
c. Digital techniques consumes more bandwidth
d. All of the above
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Part II: Short essay/problem questions (36 marks)
This part consists of 10 questions carrying a WEIGHT OF 6 marks each. You must answer
6 of these questions. You should dedicate approximately 40 minutes for this part
11- What are the environmental issues related to primary batteries?
 Very inefficient in the use of energy.
 The amount of energy used to manufacture a battery is much greater than the amount of
energy that will be usefully delivered to the equipment.
12- Define energy harvesting, provide two examples and explain one of its advantages
 Energy harvesting or scavenging is finding ways of picking up power from the environment.
 Examples include: solar power, wind power, thermal power, etc.
 The advantages are many such as: it is eco-friendly, Removes the need for providing an
energy supply ‘up front’, Reduces the amount of energy being drawn from a battery, use in
applications with different constraints (WSN for instance)
13- Explain the main advantage of EEPROM memories compared to EPROM memories
 EEPROM can be erased one bit or one byte at a time instead of being erased as a whole (such
as in EPROM)
14- Explain the principle of magneto-resistance
Magneto-resistance is a change in the electrical resistance of a conductor when it is placed in a
magnetic field.
15- What do you think is better: Compress then Code or Code then Compress? Justify your
answer
 Code then compress: Redundancy bits added by the code will be removed by the compression
and thus the result will be vulnerable to errors
 Compress then Code: Redundancy is minimized in the message signal by efficient source
coding and/or advanced data compression, and then redundancy is added back through errorcontrol coding.
 Thus compressing then adding redundancy allows the use of efficient error control codes
16- The parity-check matrix of one of the possible LDPC codes included in the standard for IEEE
802.16 (‘WiMAX’) has 2304 columns and 768 rows. What are: n, k and m?
n = 2304, m = 768 and k = 2304 – 768 = 1536
17- List the three categories of display technologies with one example on each of them
 Emissive displays: example: Plasma, CRT, LED
 Transmissive displays: example: LCD
 Reflective displays: example: e-paper
18- The wavelength of a light is between about 450 and 650nm (1nm = 10-9 m). If the speed of
light is 3 x10^8 m/s, calculate the frequency range (maximum and minimum frequencies) of
visible light?
 At 650 nm the frequency is (3 x10^8)/(650 x10^- 9) Hz, which is approximately 461
x10^12 Hz or 461 THz (terahertz).
 At 400 nm the frequency is (3 x10^8)/(450 x10^- 9) Hz = 666 x10^12 Hz or 750 THz.
19- In order to achieve high levels of compression, MPEG squeezes redundancy as possible. This
is done in two stages. Explain them.
 Spatial compression uses the fact that, in most pictures, there is usually correlation
between neighboring areas in a picture (and, hence, a high degree of redundancy in the
data directly obtained by sampling) to compress separately each picture in a video
sequence.
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
Temporal compression applies to video, and uses the fact that, in most picture sequences,
there is normally very little change during the 1/25 s interval between one picture and the
next. The resulting high degree of correlation between consecutive pictures allows a
considerable amount of further compression
20- Consider that the output of the Thresholding phase of MPEG
encoding is the following 4x4 matrix.
a. What will be the final output after the zigzag scanning
stage?
b. What will be the output of the run length-coding stage?
 The output of zigzag scanning is:
21,1,-1,0,0,0,0,1,1,1,0,0,0,0,0,0
 The output of run-length coding is: 21,0,1,0,-1,4,1,0,1,0,1,6
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Part III: Long essay/problem (54 marks)
This part consists of five questions. You must answer all the questions. You should dedicate
approximately 60 minutes for this part
21- Calculate the four figures of merit in SI units (Energy in Joules, Power in Watts, weight in kg
and volume in m3) of a battery that has the following characteristics: 1.5V (nominal voltage),
600mAh (Capacity), 16 g (weight), and 8 cm3 (Volume). The battery delivers a current of
0.8A. (12 marks)
Energy = 1.5V * 600 * 10^-3 * 3600 = 3240 J (2 marks)
Power = 1.5 * 0.8 = 1.2 W (2 marks)
Volumetric Energy Density = 3240 / 8 * 10^-6 = 405 * 10^6 J/m^3 (2 marks)
Volumetric Power Density = 1.2 / 8 * 10^-6 = 0.15 * 10^6 W/m^3 (2 marks)
Gravimetric Energy Density = 3240 / 16 * 10^-3 = 202.5 * 10^3 J/Kg (2 marks)
Gravimetric Power Density = 1.2 / 16 * 10^-3 = 75 W/Kg (2 marks)
22- Consider the following information concerning a multi-level NAND flash memory
 The following levels of charge can be distinguished: 0, C/15, 2C/15... 14C/15, C where C
represents the full charge of the transistor.
 The NAND memory cell size is 2 x10^-14 m^2
 The memory chip size is 25mm^2
Answer the following questions:
a.
b.
c.
d.
How many bits can be represented in each cell? (3 marks)
How many memory cells the memory chip contains? (3 marks)
Calculate the storage capacity of the memory in bits (2 marks)
Calculate the storage capacity of the memory in Gigabytes (3 marks)
a. n = 4 (2^4 = 16)
b. number of cells = size of memory chip/cell size = 25mm^2 / 2 x10^-14 m^2
= 25 * 10^-6 / 2 * 10^-14
= 125*10^7 cells
c. storage capacity in bits = 125 * 10^7 * 4 = 5* 10^9 bits
d. storage capacity in GB = 5 * 10^9 / (8 * 1024*1024*1024) = 5.84 GB
23- Consider the following code described as follows:
 The message size is two bits
 The codeword is five bits long
 If the message is AB (A and B are the bits of the message), the codeword for this message
is ABXYZ, where:
 X = (A) AND (B)
 Y = (A) OR (B)
 Z = (A) XOR (B)
a. Represent this code using the (n, k) representation. (2 marks)
(5,2)
b. Calculate the code rate and redundancy rate (2 marks)
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Code rate = 2/5 , Redundancy=3/5
c. Complete the following table corresponding to the code (for all possible messages) (6
marks)
Message
X
Y
Z
Codeword
(AB)
(A) AND (B)
(A) OR (B)
(A) XOR (B)
(ABXYZ)
00
0
0
0
00000
01
0
1
1
01011
10
0
1
1
10011
11
1
1
0
11110
d. Calculate the hamming distance of the code (4 marks)
00000
01011
10011
11110
00000
3
01011
10011
3
4
2
3
3
11110
Hamming distance is 2
e. How many bits this code can detect? Can correct? (3 marks)
It can detect one error bit and cannot correct any error
24- A barcode machine is reading the following full EAN-13 code (878-0121424637) and is about
to check it for eventual error. You are asked to do the check manually for an eventual error. (8
marks)
Adding together the odd digits:
8 + 8 + 1 + 1 + 2 + 6 = 26
Adding together the even digits:
7 + 0 + 2 + 4 + 4 + 3 = 20
20*3=60+26=86
Adding these two together gives 86. Taking this result modulo 10 amounts to taking the units
digit, which is 6. Finally, the check digit is 10- 6 = 4. While the received one is 7, so there is
an error on the code.
25- Using Shannon equation, what is the maximum theoretical capacity of a channel of bandwidth
500 MHz if the signal to noise ratio (SNR) is 100? (6 marks)
According to shannon: C = B log2 (1 + SNR) = 500 * 106 * log2 (1 + 100) = 500 * 106 *6.66 =
3330 Mbits/s
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