## Wireless Networks and Security

Word Counts : 3000 words

#### LEARNING OUTCOMES

The learning outcomes (LOs) for this module are:

LO1 Be able to describe, explain critically and analyse wireless data communication technology along with associated security issues.

LO2 Be able to analyse and model wireless behaviour using appropriate mathematics.

LO3 Be able to critically analyse enterprise requirements for wireless systems.

LO4 Be able to critically analyse 802.11 protocol information.

LO5 Be able to Make critical decisions about designing secure wireless networks.

LO6 Be able to understand the global nature of WLAN standards and design.

Question 1 (15 Marks)

a) Explain the concept of phase of a wave with the help of a diagram. Provide a diagram that illustrates two waves which are 90o degrees out of phase. (6 marks)

b) A wireless node receives two waves that are 180o out of phase. Critically explain how reception at the node will be impacted and what will be the result? You can use a diagram to explain your answer. (6 marks)

c) Can amplification of the two waves that are 180o out of phase help in increasing the received signal strength? Explain your answer. (3marks)

Question 2 (15 Marks)

a) Assume an isotropic radiator is radiating power 5 mW. Calculate the power density at a radial distance 200 m. Show your working steps. (4 marks)

b) Assume a non-isotropic radiator is radiating at power of 0.5 mW. Calculate the power density at radial distance of 0.3 km, where the antenna gain is assumed to be 2. Show your working steps. (4 marks)

c) 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 1/3, how would it affect the signal power seen at the receiver? Show your working steps. (7 marks)

Question 3 (20 Marks)

a) Explain the difference between the modulation schemes 16 QAM and 64 QAM? Compare the error performance of 16 QAM and 64 QAM, i.e., if the transmission takes place at 64 QAM instead of 16 QAM how will that impact the bit error rate? (5 marks)

b) If the received SNR at the receiver is 15dB and the channel bandwidth is 2 GHz, calculate the theoretical channel capacity. Show your working. (8 marks)

c) Explain the concept of pre-authentication of a mobile device for association with an access point (AP). How can pre-authentication help in roaming? (7 marks)

Question 4 (20 Marks)

a) You are a network engineer who has been asked to deploy a wireless LAN at St James Park football stadium. What will be your first step for planning the network deployment? What will be your considerations and assumptions for the network deployment? What factors will contribute to help you in making your decision regarding choosing the type of antenna for deployment? (7 marks)

b) List three common types of attack that can affect your deployed wireless LAN? (6 marks)

c) Assume that on the match day (busy day) it is raining, and users are experiencing poor quality of wireless network. What do you think is the reason(s) for poor wireless signals? Which RF signal property might have contributed to the poor signal reception? (7 marks)

Question 5 (15 Marks)

a) Explain the hidden node problem and explain the technique used by 802.11 to avoid this problem with the help of a diagram. (7 marks)

b) What are the differences between Wi-Fi Protected Access WPA version 1 WPA1 and version 2 WPA2? (8 marks)

Question 6 (15 Marks)

a) MIMO is used for transmissions in 802.11n. Explain the concept of multi-input multi-output (MIMO) and its impact on the transmissions. (7 marks)

b) Will the end-to-end transmission reliability increase or decrease if we increase the number of antenna elements at the transmitter and the receiver? Explain your answer. (4 marks)

c) What is the benefit provided by the utilisation of Target Wake Time (TWT) in 802.11ah? (4 marks)