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EXAMINATION PAPER

Module CodeKF7031
Module TitleWireless Networks and Security
ComponentExam
Module TutorNauman Aslam
Distributed onMay 17 at 9:30 am
Length of the Exam2:30 – 3:00 hrs
Weighting50%
Word LimitNoted below each question
Date and Time of SubmissionBefore 9:30 and on May 18th
Number of Pages
Additional NotesWorkings steps are required for calculation questions. Lack of derivation steps will result in 0 mark for that question.
It is your responsibility to ensure that your exam answer arrives before the submission deadline stated above.Electronic Management of Assessment (EMA): Your answer to this exam will be submitted electronically via Turnitin. You will find a Turnitin link on your module’s eLP site.There is guidance for students on how to submit assignments by Turnitin which is available on the University website at https://www.northumbria.ac.uk/about-us/university-services/it-services/it-support-365/student-it-guides/

Instructions

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You have a 24-hour window from the release of the alternative exam in which to submit your answer (via eLP).

You do not have to do the exam as soon as it is released, however, it is recommended that you only spend the time allocated for the length of the exam, for example, you spend 3 hours answering a 3-hour exam.

There is a maximum word limit for the total exam answer (see Word limits below), but this is a maximum limit, and you do not have to reach the maximum word limit if you do not need to.

Use the Answer Book Template (available in eLP) to record your answers.

You can use your textbooks and study materials (e.g. lecture notes, seminar preparation) in answering the exam questions, but to avoid plagiarism you should reference all quotes (see Academic Misconduct below).

Should you encounter a problem please contact the Exams and Awards Team ([email protected]) and the module tutor (via email)

Late submission of work

An answer for an exam that is submitted after the published submission deadline as set out above, without approval, will be regarded as not having been completed. A mark of zero will be awarded for the assessment.

The usual rule that applies to coursework and gives students a 10% penalty where work is submitted up to 24 hours after the published hand-in deadline does NOT apply here.

Any exam answer submitted after the deadline is an automatic fail.

If you have technical problems and are unable to submit your exam answer on Turnitin, you should contact [email protected] and your module tutor, and provide details of the issue, as well as your completed answers, if your email is outside normal working hours.

Word limits and Penalties

The maximum limit for this assessment is 2900 words.

Where a student exceeds this limit, the marker will stop reading when they judge that the work exceeds the limit and will indicate on the text where they stop reading. A mark will only be awarded for content up to this point.

Please note this is a maximum word limit, you do not have to use all the permitted words in your answers.

Your word count must be declared on the front page of your submission.

Academic Misconduct

The Academic Regulations for Taught Awards (ARTA) states that students are expected to observe University regulations which define and proscribe cheating, plagiarism and other forms of academic misconduct.

The University Academic Misconduct Policy is set out in the Regulations and Procedures applying to cheating, plagiarism and other forms of academic misconduct and is available at:

https://www.northumbria.ac.uk/about-us/university-services/academic-registry/quality-and-teaching-excellence/assessment/guidance-for-students/.

In submitting this assessment, you are agreeing with the following statement: ‘I have neither received nor given any unauthorized assistance on this assessment’.

You are reminded that plagiarism, collusion and other forms of academic misconduct as referred to in the regulations and procedures are taken very seriously by the University. Exams in which evidence of plagiarism or other forms of academic misconduct is found may receive a mark of zero.

Module Specific Assessment Criteria

Guidance as to how criteria will be used to determine your mark will be available on your eLP site.

Breakdown of Marks

1Question 120 Marks
2Question 220 Marks
3Question 315 Marks
4Question 415 Marks
5Question 515 Marks
6Question 615 Marks
Total100 Marks

Question 1 (20 Marks)

Note: Word limit for each question part is 150 words excluding references, equations and diagrams. (Total word count – 450)

a) In wireless communications, multipath is a common phenomenon that results in radio signals reaching the receiving antenna by two or more paths. Consider an example scenario (Figure below) in which a pair of wireless transmitter and receiver are operating at 2.5 GHz. A transmission from node A takes two paths, a direct path, and an indirect path after bouncing from the ceiling. As a result, node B receives two copies of the same signal, however, the one resulting from the indirect path is separated by a distance of 6 cm. The propagation velocity of the RF wave is 3 x 108 m/s. Critically analyse the impact of multipath in this case. Show your workings.

(8 Marks)

b) In wireless communications, how does the power of a signal change with respect to distance? Critically analyse the relationship between power seen at the receiver and the distance ‘r’ between transmitter and receiver. If the distance ‘r’ is reduced by half, how would it affect the signal power seen at the receiver? Show your workings.

(6 Marks)

c) Assume the following scenario: John Doe an Engineer from the Newcastle City Council installed a new wireless LAN in the Eldon Square shopping mall after performing a wireless site survey. After installation he measured RF signal strength and coverage and found it adequate. During the first two weeks of December 2020 (busy Christmas shopping season), bad weather forced many shoppers from the street into the mall such that it was crammed with people. Many complained about the poor quality of wireless network. During this time, the signal strength and quality of WLAN was less than desirable in many areas. What do you think is the reason(s) for poor wireless signals? Which RF signal property might have contributed to the poor signal reception?

(6 Marks)

Question 2 (20 Marks)

Note: Word limit for each question part is 200 words excluding references, equations, and diagrams. (Total word count – 600)

a) Suppose that a signal travels through a wireless transmission medium and its power is reduced to 1/8th of its original transmit power. How much of the signal power is lost in dB? Show your workings in the answer.

(6 Marks)

b) Critically compare Frequency Hopping Spread Spectrum (FHSS) and Direct Sequence Spread Spectrum (DSSS) with respect to key issues such as narrowband interference and colocation.

(8 Marks)

c) Consider the following RF transmission system (Figure below) which is designed with the impedance of the load as 40.5 Ohm and that of the source and transmission line as 50 Ohm. Find the Voltage Wave Standing Ratio (VSWR). How much Return Loss is expected for this system? By examining the values obtained for VSWR and Return Loss, evaluate the operational efficiency of this system.

(6 Marks)

Question 3 (15 Marks):

Note: Word limit for each question part is 200 words excluding references, equations, and diagrams. (Total word count – 400)

a) Assume you are working as a Network Engineer for a Telecommunications service provider and your task is to estimate the feasibility of a 20 km link between two buildings with one access point and one client radio. The access point is connected to an antenna with 12 dBi gain, with a transmitting power of 500 mW and a receive sensitivity of -84 dBm. The client is connected to an antenna with 10 dBi gain, with a transmitting power of 16 dBm and a receive sensitivity of -82 dBm. The cables in both systems are short, with a loss of 3 dB at each side at the 900 MHz frequency of operation. What is the link margin? By examining the link margin, comment on the reliability of the link.

(10 Marks)

b) IEEE 802.11n introduced few significant enhancements to the previous version (802.11g). Critically explain how these enhancements resulted in producing a wireless standard that could achieve much higher data rates?

(5 Marks)

Question 4 (15 Marks)

Note: Word limit for each question part is 150 words excluding references, equations and diagrams. (Total word count – 450)

a) Consider the scenario shown in the figure below. Any two adjacent nodes are within their transmission ranges. Let us assume that 802.11 CSMA/CA is used. Node A transmits RTS to B, which is successfully received by node B. Node B starts transmitting the CTS. At the same time when node B is transmitting, node D sends RTS to node C. Would this cause a problem? Will D be able to transmit its data to node C? If so, when and how? If not, why?

(5 Marks)

b) In a WLAN system which is using DSSS, following data 11010010001011011101 is transmitted. If 1101 is used as the spreading chip code, what was the original data? Show your workings.

(5 Marks)

c) Briefly explain which factors are important for planning a Wireless LAN design for a campus network.

(5 Marks)

Question 5 (15 Marks)

Note: Word limit for part (a) is 200 words excluding references, equations, and diagrams. Word limit for part(b), (c) is 150 words. (Total word count – 500).

a) Critically analyse the effectiveness of security enhancement proposed in the Temporal Key Integrity Protocol (TKIP). Discuss its key features and process for encryption.

(8 Marks)

b) Consider a message M which is to be encrypted with RSA algorithm. Describe the steps in the encryption and decryption algorithms, including an explanation of the symbols and terms used paying particular attention to the keys employed in encryption and decryption and the size of the message?

(3 Marks)

c) In the case of a public key with n = 55 (with p=5 and q=11) and e = 3, determine the value of private key d. Show all steps.

(4 Marks)

Question 6 (15 Marks)

Note: Word limit for each question part (a) is 300 words excluding references, equations and diagrams. Word limit for part(b), (c) is 150 words. (Total word count – 500).

a) List and critically explain at least five (05) security mechanisms that are important for wireless communications?

(10 Marks)

b) Analyse what can happen when an intruder compromises the pre-shared key (PSK) or passphrase used during WPA/WPA2-Personal authentication?

(5 Marks)

(End of Exam)

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