ELE00113M Page 1 of 8 MSc Degree Examinations 2020-1 Department: Electronic Engineering Title of Exam: Introduction to Communications Time Allowed: 24 Hours (PLEASE NOTE: papers submitted more than 30 minutes after the deadline will not be marked) Time Recommended: THREE hours Allocation of Marks: All questions carry equal marks. Instructions for Candidates: You should attempt all 3 questions. You may write all of your answers by hand, use a mix of handwritten and typed answers, or type all of your answers. Whatever method you use, you must submit your answers in a single pdf document. Use only black or blue pens for any handwritten answers. The use of red pens is forbidden and may result in questions not being marked. Clearly write or type your examination number on each page submitted. Begin each question on a new page and clearly write or type the question number on each page. More detailed instructions regarding submission of your work and conduct during the open exam is given on the next page. Please read this carefully before you begin, including the information regarding the conduct expected of you during the exam. Paper Queries: Please see the detailed instructions on the next page regarding queries to the exam setter. The exam setter for this exam is Professor Alister Burr who can be contacted by email at [email protected]. Please copy any email that you send to the Chair of Board of Examiners ([email protected]) and to [email protected]. ELE00113M University of York Page 2 of 8 A note on Academic Integrity: We are treating this online examination as a time-limited open assessment, and you are therefore permitted to refer to written and online materials to aid you in your answers. However, you must ensure that the work you submit is entirely your own, and for the whole time the assessment is live you must not: ● communicate with departmental staff on the topic of the assessment, except for the exam setter. ● communicate with other students on the topic of this assessment. ● seek assistance with the assignment from the academic and/or disability support services, such as the Writing and Language Skills Centre, Maths Skills Centre and/or Disability Services. (The only exception to this will be for those students who have been recommended an exam support worker in a Student Support Plan. If this applies to you, you are advised to contact Disability Services as soon as possible to discuss the necessary arrangements.) ● seek advice or contribution from any third party, including proof-readers, friends, or family members. We expect, and trust, that all our students will seek to maintain the integrity of the assessment, and of their award, through ensuring that these instructions are strictly followed. Failure to adhere to these requirements will be considered a breach of the Academic Misconduct regulations, where the offences of plagiarism, breach/cheating, collusion and commissioning are relevant – see AM.1.2.1” Please make sure you note the following detailed instructions: If you do not submit by the deadline you will score a mark of zero unless you submit in the first 30 minutes after the deadline in which case your mark will be subject to a 5% late penalty. The deadline is not flexible, it may take a while for your file to be processed through the system. Make sure you submit in good time to allow for this. You must submit your answers as a single pdf file. In the case of the Accounting & Finance exam, an excel file with separate worksheets for each of the questions is acceptable as an alternative to a pdf file containing handwritten answers Please check that all scanned pages are clear and visible BEFORE you submit. The Adobe Scan app is a free app that works on all phones and can be used to photograph and then connect together all the scans into a single document – ensure all your pages are in the correct order. Please make sure that every page is clearly labelled with both your examination number (NOT your name) and the question number. It would be useful if you numbered the pages. The file size limit for anonymised work submitted online is 30MB per file. Please see Compressing File Sizes (Student Guide) for details on reducing the file sizes. If your submission remains too large or if you experience genuine technical difficulties when trying to submit, then you should email your submission to elec- [email protected]. If the assessment is too large to send by email, you may use the University of York Deposit Service. If using this service as the back-up please specify [email protected] as the recipient of the drop-off. Please do not use this backup option if the VLE submission has worked properly and you have received a receipt. University policy is that corrections or clarifications to the questions in the exam paper will only be issued within the first hour of the submission window. Therefore if outside the first hour you should answer the question as best as you can and note the assumptions that you have made to allow you to proceed. All submissions may be screened for collusion and plagiarism. By submitting your assignment you agree to the University rules on Collusion and Plagiarism. The Department will run submissions through Turnitin wherever possible. For more information visit york.ac.uk/integrity You may make multiple submissions up to the assessment deadline but by default, we will mark your last submission before the deadline. ELE00113M Page 3 of 8 IT IS YOUR RESPONSIBILITY TO MA
KE SURE THAT YOUR SUBMISSION IS CORRECT. Once you have submitted your assignment via the VLE, a ‘receipt’ screen appears that has a link to the submitted file, so you can click the link and check the file to make sure it is the correct one. You can also click back into the submission point and see links to the file(s) you have submitted. ELE00113M University of York Page 4 of 8 1 (a) [12 Marks] Explain the difference between baseband and bandpass (or modulated) data transmission, giving examples of where each one might be used. (4 marks) For the data sequence ‘0110’, sketch the waveforms for each of the four combinations of unipolar and polar signalling, with return- to-zero (RZ) and non return-to-zero (NRZ), and also the waveform for polar Manchester coding. In each case also sketch the signalling pulse. (8 Marks) (b) [14 Marks] Describe the relationship between the power spectrum of a random baseband data waveform and the signalling pulse. Explain in your own words why this relationship arises. (6 marks) A baseband data transmission scheme operating at 250 kbit/s uses unipolar RZ signalling in which the signalling pulse width is one quarter of the bit period. Sketch the single-sided power spectrum of this signal, and find the maximum power spectral density at any frequency above 2 MHz, in dB relative to the power spectral density at zero frequency. (8 marks) ELE00113M Page 5 of 8 (c) [12 Marks] What is meant by intersymbol interference State the Nyquist criterion in time domain form and explain why it enables intersymbol interference to be avoided. (4 marks) Sketch, as accurately as possible, the single-sided amplitude spectrum of a raised cosine Nyquist signal with 40% roll-off. Use this plot to show that this spectrum fulfils the Nyquist criterion in frequency domain form. (6 marks) If a baseband channel has bandwidth 700 kHz, find the maximum data rate for distortion-free binary transmission using this signal. (2 marks) (d) [12 Marks] Explain why in practice a root raised cosine signal is often used. Sketch the single-sided amplitude and power spectra of such a signal, again with 40% roll-off. (8 marks) A binary signal using this format has power 0.5 pW at the receiver, and the noise power spectral density at the receiver is 5 × 10 22W/Hz. For the data rate you obtained for the system in part (c), find the maximum signal to noise ratio, in dB, that can be achieved at the detector, following any filter. (4 marks) ELE00113M University of York Page 6 of 8 2 (a) [12 Marks] Explain in your own words what is meant by noise figure and by noise temperature. How can each be used to determine the equivalent input noise power for a receiver driven from a matched impedance at 290K A receiver has a noise figure (defined at 290K) of 6 dB. Find the equivalent input noise power spectrum density, assuming it is operating at 17 C. Boltzmann’s constant, expressed in dB, is -228.6 dBJ/K (b) [12 Marks] Describe in your own words how noise can give rise to errors in a digital communication system, and how the error probability may be calculated for a given signal to noise ratio. You may illustrate your answer with reference to binary phase shift keying (BPSK), using appropriate diagrams. Hence show that for BPSK the bit error probability is given by: = (√ 2 0 ) Explain the terms in the equation. ELE00113M Page 7 of 8 (c) [26 Marks] The constellation shown in Fig 2 is for a modulation scheme sometimes called STAR-16QAM. (Note that the radius of the outer ring is twice that of the inner ring). Find a formula for the BER of this scheme in terms of the bit energy to noise density ratio, 0 , valid for high values of 0 . State any assumptions you may make. (20 marks) What simple change to the constellation might improve its BER performance Estimate approximately how much this might reduce the required power for a given very low BER. (6 marks) Fig. 2: STAR-16QAM ELE00113M University of York Page 8 of 8 3 (a) [12 Marks] List two types of antenna that can provide a large gain (10 dBi or more). For each state the parameters that determine the achievable gain, and describe how the gain might be calculated. Describe also what determines the boresight direction and the beamwidth. (b) [14 Marks] List three factors other than free space path loss that may cause attenuation to a radio signal as it passes through the atmosphere. At which frequencies in which geographical locations may each be particularly significant (9 marks) A radio link operating at 60 GHz is subject to atmospheric attenuation of 20 dB/km. Compare the atmospheric attenuation to the path loss for a link of length 10 km. Comment on the result. (5 marks) (c) [24 Marks] A radio link receiving signals from an interplanetary spacecraft operates at 8 GHz. The antenna on the spacecraft has a gain of 20 dBi, and it transmits with power 1W. The terrestrial receiving antenna is a dish of diameter 50 m, and you may assume the aperture efficiency is 70%. The antenna receives sky noise at an effective temperature of 6K, and the receiver has a noise temperature of 20K (it is cooled in liquid helium). The data rate should be 64 kbit/s, and the demodulator requires a bit energy to noise density ratio of 10.5 dB for correct operation. Determine the link budget and hence find the range of the link. (18 marks) Without changing the antennas or the transmit power, how might the range be increased (6 marks) Boltzmann’s constant is -228.6 dBJ/K End of Paper