MSc IntroComms Paper 2 2010SummerExamPaperAndSolution[1]

COLLEGE OF ENGINEERING AND PHYSICAL SCIENCES ELECTRONIC , ELECTRICAL & COMPUTER ENGINEERING

IntroComms Introductory Module for Communications Paper One

2009/10 January Examination Paper and Specimen Solutions

A24942 / A24955

Calculators may be used in this examination but must not be used to store text. Calculators with the ability to store text should have their memories deleted prior to the start of the examination Special Requirements: Multiple Choice Answer Grid

College of Engineering and Physical Sciences School of Electronic, Electrical and Computer Engineering Degree of M.Sc. Communications Engineering Satellite and Mobile Communications Communications Networks Electronic and Computer Engineering Embedded Systems Interactive Digital Media also with Industrial Studies

04 21480 INTRODUCTORY MODULE FOR COMPUTING and 04 21487 INTRODUCTORY MODULE FOR COMMUNICATIONS PAPER ONE January Examinations 2010 Time Allowed: 1 hour 30 minutes

Candidates should attempt TWO questions

All questions carry equal marks

The marks allocated to each part of each question are shown in square brackets in the right-hand margin.

A24942 / A24955 1.

2.

Any Calculator

(a)

Briefly describe the four main user centred design activities, as identified by the ISO 13407 standard. Use a simple block diagram to show their interdependence. [5]

(b)

Identify and describe the main elements that constitute a use-case textual description. [5]

(c)

Define the term “requirements engineering”. Which are the two main types of activities that take place during the requirements phase of a software engineering project? [5]

(d)

Describe the main purposes for which a UML-based activity diagram can be used for object-oriented analysis and design. Create an example diagram to explain all the expected elements of graphical notation that can be used for this type of diagrammatic representation. [5]

(a)

(i)

What are the typical bandwidths of a Hi-Fi signal and an analogue, PAL colour TV signal? [2]

(ii)

Suppose a communication signal has a power of 10 mW and the equivalent noise power is 20 µW. Calculate the signal to noise ratio. [1]

(iii)

State the advantages of coaxial cable over twisted pair cabling.

(i)

If a telephone line carries a call for 30 minutes what is the amount of telephone traffic in Erlangs? [1]

(ii)

State two different forms of multiplexing as used in a telephone network.

(b)

(iii)

[2]

[2]

Voice signals are to be transmitted down a fibre optic cable using an analogue-to-digital converter with 6 bits. Assuming Pulse Code Modulation is used and that 22,000 separate voice signals are sent down the same cable, what is the minimum bit-rate required to transmit all signals? [2]

Question 2 continued over

A24942 / A24955

Any Calculator

Question 2 continued (c)

The Fourier transform and inverse Fourier transform of an energy-limited signal g ( t ) are given by, ∞

G( f ) =

∞

∫ g ( t ) exp ( − j2

π

−∞

ft ) dt and g (t ) =

∫ G ( f ) exp ( j2

π

ft ) df ,

−∞

respectively. The following expression represents a radio frequency pulse,  t  g ( t ) = A rect   cos ( 2π f c t )  T  where rect ( t ) is the unit rectangular pulse function defined as,

1, − 12 < t < 12 rect ( t ) =  . 1 0, t > 2 

(d)

(i)

Determine the Fourier transform of rect ( t ) .

[2]

(ii)

State the Fourier transform time-scaling property.

[1]

(iii)

State the Fourier transform frequency shifting property.

[1]

(iv)

What is the Fourier transform of g ( t ) ?

[1]

(i)

State Shannon’s channel coding theorem (2 nd theorem).

[1]

Alphanumeric data are entered into a computer from a remote terminal through a voice-grade telephone channel. The channel has a bandwidth of 3.4 kHz and an output signal-to-noise ratio of 20 dB. The terminal has a total of 128 symbols. Assume that the symbols are equi-probable and that successive transmissions are statistically independent. (ii)

Calculate the information capacity of the channel.

[2]

(iii)

Calculate the maximum symbol rate for which error-free transmission over the channel is possible. [2]

A24942 / A24955

3.

(a)

Any Calculator

The multiple choice questions in this section should be answered on the grid at the end of this paper. The grid should be submitted with the answer book.

(i)

Which of the following CANNOT be implemented as a basic type in ANSI standard C, but must be implemented using other datatypes? [2] A. B. C. D. E.

(ii)

Bits. Bytes. Integers. Floating point. Characters.

Consider a 10x10 array where each element will represent the colouring of a 10x10 board with black and white squares. The following loop will colour in the squares, what pattern will it produce? [2] f or ( i =0; i <=9; i ++) f or ( j =0; j <=9; j ++) i f ( ( ( i +j ) %2) ==0) ar r ay[ i ] [ j ] = bl ac k; el se ar r ay[ i ] [ j ] = whi t e;

A. Alternating black and white rows. B. Black diagonals, all other squares white. C. Alternating black and white patterns (chessboard or checkerboard). D. Subgroups of alternating 2x2 black and white squares. E. None of the above.

(iii)

Consider the following program. What output is produced?

[2]

voi d my_ f unc t i on ( i nt a, i nt b, i nt c ) { a+=10; b+=10; c+=10; } i nt mai n( voi d) { i nt x=0, y=10, z=20; my_f uncti on ( x, y, z) ; pr i nt f ( “%d %s %d”, x, y, z) ; r et ur n 0; }

A. B. C. D. E.

0 10 20 10 20 30 20 30 40 10 10 10 20 20 20

Question 3 continued over

A24942 / A24955

Any Calculator

Question 3 continued (iv)

Consider the following program in which the programmer has made an error with respect to memory allocation. [2] i nt x = 10, *p = mal l oc(5, si zeof ( i nt ) ) ; p = &x;

The error is A. B. C. D. E. (v)

Which of the following statements about a “while” loop is (are) TRUE? A. B. C. D. E.

(b)

Static allocation. Dynamic allocation. Memory leak. Memory overflow. Dangling pointer.

[2]

The body of a “while” loop is always executed at least once. A “while” loop can always be replaced by a "for" loop. “While” loops cannot be used with 2-D arrays. A “while” loop is functionally identical to a “do-while” loop. All of the above.

A program is being developed in the C programming language to store a 256x256 grid of pixels of a colour screen display. Each pixel can store a value between 0 and 65,535 (16 bits), representing the colour of that pixel. (i)

Write down a suitable declaration in the C programming language for the screen (hint - you may assume that the short datatype is 16 bits). [2]

(ii)

Write down code in the C programming language (or suitable pseudo-code) to invert the screen (as seen by a user). Minor syntactic errors will not be penalised.

(iii)

[5]

Comment on the additional steps, or additional information that may be required, if this program were to be implemented on an actual embedded system with video memory. [3]

School of Electronic, Electrical and Computer Engineering

Introduction to Computers and Introduction to Communications Part 1 Answer sheet for multiple choice question 3 (a) Shade one cell on each row to indicate your answer. Any cases where more than one cell on a row appears to be marked will result in a mark of zero. When completed attach this sheet to your answer book with a treasury tag for submission.

Student ID:

Answers Question 3

A (i)

(ii)

(iii)

(iv)

(v)

B

C

D

E

Module: Type: ELECTRONIC , ELECTRICAL & COMPUTER ENGINEERING

Year: Sessional

Level:

Question:

2009-10

Examiner:

LM

Marks allocated: 20 /20

1 TNA

Page 1 / 3

SOLUTION TO EXAMINATION QUESTION Module Code:

Ac. Year:

Type:

Level:

Examiner:

2009-10

Sessional

LM

TNA

(e.g. 2009-10)

(Sessional/Resit/Special)

(e.g. LC)

Question No:

1

Part Solution 1a

Marks allocated

There are four iterative design activities which are part of the user design process that is described by the ISO 13407 Standard: 1. Understanding and specifying the Context of Use

1

2. Specifying the user and organisational requirements

1

3. Producing design solutions

1

4. Evaluating the design against requirements

1

The following block diagram shows the interdependencies of the above mentioned activities:

1

1b

A use case textual description will generally include the following elements: 1. Name of the use case: A descriptive name of the use case is specified. In this element one can add some general comments and notes that might be describing the use case. 2. Actors: In this element, all the actors that are part of the use case are identified and named.

1

1


Year: Sessional

Level:

2009-10 LM

Question: Examiner:


1 TNA

Page 2 / 3

SOLUTION TO EXAMINATION QUESTION – Continuation Sheet

Part Solution

3. Requirements: Things that the use case must allow the user to do. 4. Constraints: Rules about what can and can’t be done. This can include preconditions that must be true before the use case is run; post-conditions that must be true once the use case is run; invariants: these are conditions that are always true. 5. Scenarios and Scenario diagrams: Sequential descriptions of the steps taken to carry out the use case. May include multiple scenarios, to cater for exceptional circumstances and alternate processing paths. Scenario diagrams usually include sequence diagrams to depict the workflow - similar to scenarios but graphically portrayed. 1c

Marks allocated 1

1

1

The following definition is based on Pohl, K., 1993, The three dimensions of th requirements engineering, 5 International Conference on Advanced Information Systems Engineering and was given to the students during the lectures. A similar definition is expected: “Requirements Engineering can be defined as the systematic process of developing requirements through an iterative co-operative process of analysing the problem, documenting the resulting observations in a variety of representation formats, and checking the accuracy of the understanding gained.”

3

The main two types of activities that take place during the requirements phase of a software engineering project are:

1d

1. Problem Analysis

1

2. Problem Description

1

It is expected that the students provide a similar answer on this part of the question The main purposes for which a UML-based activity diagram ca n be used for objectoriented analysis and design are: – – – –

to model a task (for example in interface interaction) to describe a function of a system represented by a use case to describe the logic of an operation to model the activities that make up the life cycle of a project

2


Year: Sessional

Level:

2009-10 LM

Question: Examiner:


1 TNA

Page 3 / 3


Part Solution

Students are expected to provide an example with the following elements of notation: main element is that of representing actions by using a two-dimensional symbol - rectangle with rounded corners- and that of control flows, which are represented by arrows with open arrowheads. Also, the notation includes the concept of initial node (black circle), decision nodes and merge nodes (diamond), guard conditions (text in square brackets) and final node (black circle inside a white circle). Advanced notation can use fork and join nodes to describe cases that have actions that happen in parallel – assigning ½ marks per element (grouped as underlined).

Marks allocated

3

Module:

04 21487

Year:

Type:

Sessional

Level:

Question:

2009-10

Examiner:

M

ELECTRONIC , ELECTRICAL & COMPUTER ENGINEERING


2 PAS & CCC

Page 1 / 3

SOLUTION TO EXAMINATION QUESTION Module Code:

Ac. Year:

04 21487

Part

Type:

Level:

Examiner:

2009-10

Sessional

M

PAS & CCC

(e.g. 2009-10)

(Sessional/Resit/Special)

(e.g. LC)

Question No:

2

Marks allocated

Solution

(a) (i) Hi Fi BW=15-18 KHz Colour TV BW=5-6MHz

1 1

(a) (ii) 37dB

 PS  0.01   dB = 10 log10     0.00002   PN 

SNR = 10 log10 

(a) (iii)

State the advantages of coaxial cable over twisted pair cabling Coaxial has: More BW More resistant to EMI Usually less lossy 2 from 3 acceptable

1

2

(b) (i) 1 call for 1 hour = 1erlang so answer=0.5 Erlangs

1

(b) (ii)

Frequency Multiplexing and Time Domain Multiplexing

2

(b) (iii)

ADC 6 bits, 256 samples PCM Voice signal, so BW about 3.5 KHz, so sampling frequency approx 8KHz 8KHz*6=48Kb/s 0.048Mb*22000=1056Mb/s

2

(c) (i) The Fourier transform of s ( t ) = rect ( t ) is given, by definition, by, ∞

S( f )=

∫ rect ( t ) exp ( − j 2

π

ft ) dt

−∞

12

=

∫ exp ( − j 2

π

−1

=

=

(c) (ii)

ft ) dt

2

1

12

− j 2π f

exp ( − j 2π ft ) −1 2

sin (π f ) f

π

g ( at ) =

1 a

2

= sinc ( f )

 f   a

G

1

Module:

04 21487

Year:

Type:

Sessional

Level:

2009-10 M

Question: Examiner:



2 PAS & CCC

Page 2 / 3

SOLUTION TO EXAMINATION QUESTION – Continuation Sheet Marks allocated

Part

Solution

(c) (iii)

g ( t ) exp ( − j 2π f c t ) = G ( f − f c )

(c) (iv)

Using (ii), we have, g ′ ( t ) = A rect ( t T ) ⇒ G′ ( f ) = AT sinc ( f T )

1

Using (iii), we have, g (t ) = G ( f ) = =

(d) (i)

 exp ( − j 2π f ct ) + exp ( j 2π f ct )   t  A rect   cos ( 2π f ct ) = g ′ ( t )   2  T    G′ ( f − f c ) + G ′ ( f + f c )

2 AT

2

{sinc ( f − f

c

) T  + sinc ( f

+

0.5

f c ) T }

Shannon’s channel coding theorem (2nd theorem) states that, for a source of entropy H emitting a symbols every T S seconds through a channel of capacity C bits/symbol capable of transmitting a symbols every T C seconds: A If H / TS ≤ C / TC there exists a coding scheme with an arbitrarily small probability of error (equality implies signalling at the critical rate) B If H / TS > is not possible to transmit information over the channel and C / TC it reconstruct it with an arbitrarily small probability of error

(d) (ii)

1 either A or B on their own are OK

The information capacity rate of the channel is given by, C ′ = B log 2 (1 + SNR ) = 3.4 ×10 =

(d) (iii)

0.5

3

log 2 (1 + 10

22.6 ×10

3

20 10

)

2

bits/second

Acording to (i) a), H max / TS = C / TC , with the r.h.s. being equal to C’ from (ii). Thus, C ′ 1 Symbol rate = . = TS H max

Since H max = log 2 k = log 2 128 = log 2 27 = 7 Symbol rate =

22.6 ×103 7

bits/second

bits/symbol

= 3234

1

bits/symbol , we have

symbols/second

1

Module:

04 21487

Year:

Type:

Sessional

Level:

2009-10 M

Question: Examiner:



2 PAS & CCC

Page 3 / 3


Part

Solution

Marks allocated

Question:

3

Examiner:

SP

Module:

04 21487

Year :

2009-10

Type:

Sessional

Page:

1/2



SOLUTION TO EXAMINATION QUESTION Question No:

Module Code:

3

04 21487

Year:

Type:

Examiner:

2009-10

Sessional

SP

(Sessional/Resit/Special )

Marks allocated

Part Solution (a)

(b) (i)

(i) (ii) (iii) (iv) (v)

A C A C B

2 2 2 2 2

A program is being developed in the C programming language to store a 256x256 grid of pixels of a colour screen display. Each pixel can store a value between 0 and 65,535 (16 bits) which represents the colour of that pixel. Write down a suitable declaration in the ANSI C programming language for the screen ( hint - you may assume that short is 16 bits) [Any one of the following for 1 mark] short int screen[256][256]; short int *screen; short screen[256][256]; short *screen; unsigned short screen[256][256]; unsigned short *screen;

(b) (ii)

2

Write down code in the C programming language (or suitable pseudo-code) to invert the screen (as seen by a user) (Minor syntactic errors will not be penalised). Example of C code solution (declarations not required): for (i=0; i<=255; i++) for (j=0; j<=255; j++) { temp = screen[i][j]; screen[i][j] = screen[255-i][255-j]; screen[255-i][255-j] = screen[i][j]; }

Example of pseudo-code solution (declarations not required):

Loop i from 0 to 255 Loop j from 0 to 255

5

Question:

3

Examiner:

SP

Module:

04 21487

Year :

2009-10

Type:

Sessional

Page:

2/2




Part Solution

Marks allocated

swap screen(i,j) with screen(255-i, 255-j) End loop j End loop i [5 marks for either of the above forms. Marks to be reduced depending on the level of completeness or functionality].

(b) Comment on the additional steps, or additional information that may be (iii) required, if this program were to be implemented on an actual embedded system with video memory. On an actual embedded system, video is frequently be ma pped to an actual memory address. Here the declaration in part (i) cannot be directly used to control the video memory. 3 On some systems video may be “paged” from main memory, and a system call to switch the video to the current page, or to set page addresses, may be needed. The system discussed in the question is 16 bits. In order to develop a full set of routines the programmer would need to know the representation (allocation of bits) for red, green and blue within a 16 colour format. Timing is important – the updates to video memory need to be synchronised with the video clock or interlacing system. [3 marks for any three of the above reasons]

MSc IntroComms Paper 2 2010SummerExamPaperAndSolution[1]

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