辅导案例-ELEC6217-Assignment 1

  • May 15, 2020

ELEC6217 Radio Communications Engineering Assignment 1 Submission Details This assignment forms your first assessment for the “ELEC6217 Radio Communications Engi- neering” and contributes 15% of your mark for the module. You are required to produce a brief report, which needs to include the signal plots and your answers and anlaysis to questions 1 to 6 below. The report should be in pdf format. It is suggested that in the report you use the same section order as in this document to present your answers to the questions. Each figure in your write-up should have well labelled axes and a relevant title or legend that identifies which signals/systems are shown. Although you may verbally discuss your ideas with your classmates, you should not show them your Matlab code, figures, calculations or text. When you are finished, you need to submit your report at C-BASS: https://handin.ecs.soton.ac.uk/handin/1920/ELEC6217/1/ before 4pm on Friday 25 Oc- tober 2019. You only need to make an electronic submission. Please note the department regulations on late submissions. The marks distribution for each question is shown next to the question number below, where the marks add up to 15. If you notice any mistakes in this document or have any queries about it, please email me at [email protected] Mohammed El-Hajjar Learning Outcomes 1. Simulate communication systems using computational baseband models; 2. Produce quality technical writing such as reports and reviews. 1 Table 1: Marking Scheme Accuracy of results: Are the obtained results correct? Is the formulation correct? Are the plots accurate? Do you include all required plots? 50% Interpretation of results: How well are the questions posed in the assignment answered? Do you answer all parts of the questions? Do you include the required analysis? 30% Presentation of results: How well are the designs explained, the plots labelled and their contents discussed? Do you include all correct labels? Do you use the right label units? Do you explain your results when requested? 20% This assignment uses a Matlab file “DigiTrans.m” for simulation of a digital transmission scheme using 16-QAM modulated data. You can find this simulation file and other functions called by it in the file “assign1Files.zip” on the module notes page here. Before answering the questions below, make sure you understand the practical idea of a digital transmission scheme and its issues and then familiarise yourself with the Matlab files in the “assign1Files.zip” and understand the process of simulating a digital communications system. Note that some parameters in “DigiTrans.m” need to be adjusted in the following questions. 1. Run ‘DigitTrans.m’ and view the eye diagram of the received data prior to sampling the signal. From this diagram, you should be able to determine the exact initial sampling point Ninit. Try modifying this value and observe the effect that this has on the constel- lation pattern of the received symbols. What is the optimum value for Ninit? You should explain your answer and include the figures output of your simulation. (2 marks) 2. Modify the channel signal to noise ratio (SNR) to 20 dB,10 dB and 5dB, and observe the effect on the eye diagram and the received constellation pattern. Obtain plots of the eye diagram for the different SNR values and comment on them. (2 marks) 3. Adjust the SNR to 1000 dB (in other words, noise-free) and incorporate a dispersive channel, e.g. by setting c = [1 0 -.7] and c = [1 0 -.8]. Note that you may have to re-adjust Ninit as you may observe from the eye diagram. Obtain plots of the eye diagram and constellation diagram and comment on them and on the Ninit values. (2 marks) 4. Determine the bit error ratio (BER) (also called the bit error probability) for the noiseless case (SNR=1000dB), and SNRs of 20 dB (typical SNR of a fixed wireless channel), 12 dB, and 6 dB (typical mobile channel). You will have to alter a constant in the program to get answers that are not 50% BER (i.e. random)! Explain what parameter you had to change and what value you used and then comment on any practical problems you think there are in verifying by simulation the performance of a system with very small BER values (i.e. less than 10e-5)? (2 marks) 5. Add a function to the Matlab code to introduce a simulation of carrier frequency offset of -1/70 symbol frequency (i.e. a frequency offset below the simulation carrier frequency of 0Hz). Show a plot of the simulation for 50 symbols only (this is to make it easy to mark) and justify by inspection of the constellation diagram that the offset has been correctly applied. (3 marks) 2 6. Add a function to the Matlab code to estimate the value of Ninit (the optimum sampling point). The function may use many data symbols to form the estimate. Do not use any information such as timing or the noiseless signal from the transmitter part of the simulation, it is not available to a distant receiver. Show your results as a set of three histograms (one for each value of SNR) showing the distribution of Ninit for each SNR value. Note that Ninit is expected to be correct for all values of SNR above 10dB, so concentrate your results in the region of SNR below 10dB. (4 marks) 3

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