I‘IFIITI’IBIH UNIVERSITY

OF scuznce nnD TECHI‘IOLOGY

Faculty of Computing and Informatics

Department of Computer Science

QUALIFICATION: BACHELOR OF COMPUTER SCIENCE HONOURS

QUALIFICATION CODE: OSBCHCLEVEL: 8

COURSE: MOBILE NETWORKS AND

ARCHITECTURESCOURSE CODE: MNA81OS

DATE: JULY 2017 SESSION: 2

DURATION: ZHOURS MARKS: 100

SUPPLEMENTARY/SECOND OPPORTUNITY EXAMINATION QUESTION PAPER

EXAMINER(S): PROF DHARM SINGH JAT

MODERATOR:DR LINOH MAGAGULA

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THIS QUESTION PAPER CONSISTS OF THREE PAGES

(Excluding this front page)

INSTRUCTIONS

Write clearly and neatly.Write all your answers in the answer booklet provided.Number the answers clearly.

This paper consists of two sections; Section A and B.

Answer ALL questions in section A.

Answer any 3 questions in section B.

Begin each section on a new page.

Marks/scores per question are given in H.

Do not use or bring into the examination venue books, programmable calculators,

mobile devices and other material that may provide you with unfair advantage. Should

you be in possession of one right now, draw the attention of the examination officer or

invigilator.10. NUST’s examination rules and regulations apply.

SECTION A

[40Marks]

This section contains two questions.

Attempt all questions.

Q1

Q2

8)

b)

b)

Explain functions of the Physical layer and Data link layer in a wireless and

mobile environment.

- 2 marks for each correct statement for each layer

(i). Give 4 advantages of wireless LANs.

(ii). Give 4 disadvantages of wireless LANs.

- one mark for each advantage- one markfor each disadvantage

What are the differences between Ad-Hoc and infrastructure mode?

Explain.- two marks for each correct statement.

Describe 4 multiplexing techniques in wireless communication.

Give an example for each technique.- three marks for each multiplexing technique.

Describe how CSMA/CA solves the Hidden and exposed terminals

problems.- two marks for each correct statement.

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SECTION B

[60Marks]This section contains four questions

Attempt any three questions.

QB a)

bl

Q4 a)

b)

C)

Q5 a)

bl

If a total of 33 MHz of bandwidth is allocated to a particular FDD cellular

telephone system which uses two 25 kHz simplex channels to provide full

duplex voice and control channels, compute the number of channels

available per cell if a system uses

(i). One-cell reuse

(ii). four-cell reuse

(iii). seven-cell reuse

A total of 33 MHz of bandwidth is allocated to a particular FDD cellular

telephone system which uses two 25 kHz simplex channels to provide full

duplex voice and control channels. If 1 MHz of the allocated spectrum is

dedicated to control channels, determine an equitable distribution of

control channels and voice channels in each cell for each of the three

systems.

(i). One cell reuse

(ii). four-cell reuse

(iii). Seven-cell reuse

What is a good code for CDMA?

Explain how multipath propagation affects signal quality.

Consider a sender A wants to send the data bit 1 with key = 100101 and a

sender B wants to send the data bit 0 with key = 010110. Assume we code

a binary 0 as -1, a binary 1 as +1. Both signals are transmitted at the same

time. The noise to the transmitted signal is (0, +1, -1, 0, 0, ~1).

(i.) What signal is received by a receiver?

(ii.) What can the receiver detect for sender A and B respectively?

Why is hexagonal cell shape preferred over square or triangular cell shapes

to represent the cellular architecture?

What would be the minimum distance between the centers of two cells

with the same band of frequencies if cell radius is 1 km and the reuse factor

is 12?

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06

C)

d)

a)

Generate orthogonal variable spreading factor (OVSF) code from a set of

orthogonal codes for UMTS communication systems which are primarilyused to preserve orthogonality between different channels in a

communication system.

Assume the root has depth 0 and depth of the tree is 4.

[Each correct depth = 1 Mark]

Illustrate how fixed TDM patterns are used to implement multiple access

and a duplex channel between a base station and mobile station in DECT

cordless phone system.

Discuss the two spread spectrum techniques with the help of a diagram.

Network and signaling are crucial aspects of any cellular mobile

communication network.

i) Describe the roles of the VLR and HLR.

ii) Give two roles of the MSC in a GSM network.

GOOD LUCK

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A