Answer each of the questions listed below. You will be able to find useful information for some of the questions in the lecture notes. Other questions will require some research - perhaps using the Internet and library resources. Yet other questions are based on the practical work you completed on the LPRN. Carefully read each question and ensure that you answer each specific point. The number of marks is associated with each question; this provides some indication of the difficulty of each question and the required length/depth of your answers. The marks sum to 100, representing 40% of the assessment of this module. Academic Misconduct This is an individual piece of work - do not collude with other class members. If you wish to quote the work of others in your answers, use " " marks and provide references to your sources. Please read the University guidelines on Academic Misconduct. Submitting the unattributed work of others may result in the application of severe penalties. Learning Objective addressed by this Assignment Analyse and solve problems in wide-area and wireless networks and critically evaluate the effectiveness of various technologies, tools and methods. Questions Question 1 (marks 10) A technique known as Antenna Diversity is adopted in modern WLAN access points. 1. Explain what undesirable behaviour of radio frequency propagation diverse antannas are designed to combat (your answer should be illustrated to show signal paths). [4 marks] 2. Why may this problem be more acute when stations are mobile? [2 marks] 3. Explain how diverse antenna systems improve the performance of WLAN equipment. [4 marks] Question 2 (marks 5) The effective bandwidth of an 802.11b network is less than the 11Mbps quoted for the physical layer. 1. What are the reasons why the effective bandwidth of 802.11b networks may fall far short of 11 Mbps raw data bit rate at the physical layer? [3 marks] 2. What loss in bandwidth may result from each overhead identified above? [2 marks] Question 3 (marks 10) Fragmentation of 802.11 messages introduces additional overheads but may improve overall throughput by avoiding the loss (and retransmission) of long frames. 1. Under noisy RF conditions, how would you expect network throughput to vary as the fragment size is increased from very short to very long? [6 marks]. 2. Draw a simple graph of throughput v fragment size to support your answer - you should consider the competing influences of greater overheads for shorter messages and increased losses as a result of the retransmission of long frames which might suffer interference. [4 marks]. Question 4 (marks 20) The current implementation of LPRN uses physical carrier detection. The NAV field in the LPRN frame is unused in the current "00" implementation. 1. How is physical carrier detection is employed in current LPRN receivers? Your answer should include code fragments in C to illustrate how a receiver determines if the channel is free. [10 marks] 2. Explain, in principle, how the NAV field may be utilised to implement Virtual Carrier Detection. [10 marks] Question 5 (marks 20) Most of the fields in an LPRN frame are bit-stuffed. 1. Explain the purpose of bit-stuffing in LPRN. [5 marks] 2. Provide a commentary and listing of the function which reads an octet from the data stream, discards stuff bits and resynchronises the receiver. [10 marks] 3. Why is bit-stuffing not required in the PRE and SFD fields? [5 marks] In your written response, clearly separate your answers to each question and list the sources of information you have used to answer each question.