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1 COMMUNICATION SYSTEMS AND WIRELESS TECHNOLOGIES School of Engineering, LSBU Communication Systems and Wireless Technologies EEE_6_CWT Lab Manual Ya Bao 2 COMMUNICATION SYSTEMS AND WIRELESS TECHNOLOGIES Contents Health & Safety

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1 COMMUNICATION SYSTEMS AND WIRELESS TECHNOLOGIES School of Engineering, LSBU Communication Systems and Wireless Technologies EEE_6_CWT Lab Manual Ya Bao 2 COMMUNICATION SYSTEMS AND WIRELESS TECHNOLOGIES Contents Health & Safety..........................................................................................................................3 Guidelines for Laboratory Logbooks.........................................................................................4 Lab Report Guidelines...............................................................................................................5 The brief of Part 1 Logbook for 5 labs ......................................................................................6 The brief of Part 2 formal report is:...........................................................................................6 Submission Deadline .................................................................................................................6 CW marking scheme..................................................................................................................7 Lab 1. Amplitude modulation in Simulink .............................................................................10 Lab 2. Investigate FM modulation in Multisim.......................................................................15 Lab 3. BPSK and BERTool ....................................................................................................18 Lab 4. RF Effects on Communication System Performance ...................................................23 Lab 5. Build oscillators in Multisim ........................................................................................25 Mini-Project 1. Investigate RF Satellite Link .........................................................................30 Mini-Project 2. Reducing the Error Rate .................................................................................36 3 COMMUNICATION SYSTEMS AND WIRELESS TECHNOLOGIES Health & Safety The following items are not in any particular order of importance, so please READ THEM ALL. 1. Read all the health and safety notices on the lab notice board. 2. Put all coats and bags out of the way under the workbench or by the coat hangers. 3. No personal audio systems can be used in the lab (this includes mobile phones). 4. No running in the lab 5. Note the positions of fire extinguishers for use in an emergency only 6. Note that there are two exits from the lab 7. In case of a fire alarm, exit through either lab door and walk down the stairs following the fire exit signs. One set of stairs is near the rear lab door, check these as soon as possible. Do not use the lift. 8. Do not move or attempt to repair any equipment. All faults or queries must be reported to the technician. 9. Do not work in the lab on your own 10. Note that it is impossible to be locked in. All locks have a quick release mechanism operational from inside the lab. 11. Keep fingers away from mains outlets. 12. Note where the electricity supply stop buttons are. Use only in case of an emergency. 13. If you suspect someone is being electrocuted do not touch them but immediately hit the red stop button after which then you can attend to them and call for assistance. 14. If any medical emergency arises, call for help, there will always be a trained first-aider nearby. 15. Please be very careful when using electrolytic (polarised) capacitors as they can explode if connected with the wrong polarity. 16. If you smell burning, immediately turn off the supply to your circuit and resist the temptation to touch any components. Short-circuited integrated circuits and resistors can easily burn you. Wait a short while before checking (the components will remain warm for a minute or two). 17. Do not eating/drinking in the lab. 4 COMMUNICATION SYSTEMS AND WIRELESS TECHNOLOGIES Guidelines for Laboratory Logbooks For each lab, the logbook starts from Lab number, Lab title, date of the lab 1. AIM Write your own aim based upon that in the laboratory sheet OBJECTIVES You may copy the objectives from the laboratory sheet. 2. INTRODUCTION AND BACKGROUND THEORY A short introduction or description may be included to give a little more information about the exercise. Theory section presents theoretical models, equations, physical principles, etc., that are relevant to the investigation described in the report. It should be within one page. 3. EXPERIMENTAL a) Procedure: Follow the instructions and explain what you are doing as the experiment proceeds. b) Circuit diagram: Clear well labelled circuit diagrams are very important. c) Meter readings and measurements: Meter readings should be clearly written and tabulated if necessary. Don’t forget to include the units and estimated error margins. d) Calculations: Any formulae used should be quoted and the calculated results doubled underlined to make them ‘stand out’. Don’t forget to include the units and estimated error margins. e) Graphs: Label fully including the axis. f) Oscilloscopes: Take screen shots of oscilloscope displays and attach to the logbook at the relevant points. Label fully. 4. ANALYSIS/DISCUSSION (most important part) Comment upon the results. You need to show that you have understood the experiment and not just obtained a set of results. When comparing results e.g. a meter reading with a calculation, write the results together or tabulate them so that the reader can also make a comparison. Use visual ways of presenting results e.g. graphs. Always comment and where possible explain the shapes of the graphs or the prints of oscilloscope displays. 5. QUESTIONS Answer any questions at the end of each section. Use your results, graphs and diagrams to help answer the questions where possible. 6. CONCLUSIONS Write a short conclusion based upon the objectives and what you have learned from the experiment. For the whole logbook file, a cover page (including module title, academic year, student name and ID, course) and contents page are essential. Save logbook for ALL labs into a single pdf file then submit to VLE before the deadline. 5 COMMUNICATION SYSTEMS AND WIRELESS TECHNOLOGIES Lab Report Guidelines Formal lab reports should be typed on A4 paper and contain the following sections and don’t exceed the limit of the length. ? Cover Page: Title of the experiment, Author’s name and student number. Your instructor's name. The date of the experiment and the date of the report was prepared. ? Aims and objectives What was the purpose of the experiment? What was it supposed to reveal? ? Materials List everything needed to complete your experiment. ? Introduction and Background Theory The introduction should give some background on the problem your experiment investigated. Theory section presents theoretical models, equations, physical principles, etc., that are relevant to the investigation described in the report. It should be within one page. ? Methods/Procedure Describe the steps you completed during your investigation. Don’t simply copy the instructions given in the lab manual. You need to describe what YOU did. Make good use of diagrams, sketches, or photographs to show important layout, wiring and connections ? Experimental Results and explanations Present your results and summarise the data using figures and tables. Each figure and each table must have a number and a caption. Do not simply dump a bunch of graphs and tables into this section with no explanation. It is best to locate figures and tables within the text (and preferably on the same page where they are referred to) rather than grouping them together at the end of the report. ? Discussion Discuss the meaning and importance of the experimental results, compare the results to theoretical predictions, describe the accuracy of the results, address discrepancies, and ultimately draw conclusions in regards to the objectives of the experiment. ? Conclusions and Recommendations This section summarizes the conclusions that have been made and gives specific recommendations for the next steps that could be taken in subsequent experiments or further research. ? References If your research was based on someone else's work or if you cited facts that require documentation, then you should list these references. 6 COMMUNICATION SYSTEMS AND WIRELESS TECHNOLOGIES The brief of Part 1 Logbook for 5 labs 1. The aim of Part 1 is to Familiar Matlab (Simulink) and Multisim used for communication systems. 2. The objectives of Part 1 coursework are Build communication systems in Simulink and Multisim Investigate system performance Analyse simulation results and summary your conclusions. 3. You are required to build and configuration system models in the software and analyse simulation results. 4. The design and simulation procedures should follow what you have learned from Communication systems and Wireless Techniques lectures. 5. System design, setting, simulation results, analyses / discussions and conclusions need to be included at the logbook. 8. The length of the Part 1 logbook should be within 30 pages. The brief of Part 2 formal report is: 1. The aim of Part 2 coursework is to apply the knowledge learned from the class to start a simple research work. 2. The objective of Part 2 coursework is to design and build a communication system on a simulation platform to investigate the system performance. 3. You are required to work on a communication system built on Simulink to deeply investigate key factors which affect the performance of the whole system. Comparations, discussions and theorical analyses are essential. 4. The design and implementation procedures should follow what you have learned from Communication systems and Wireless Techniques lectures. 5. You can develop the software on you own selected language but that need to be approved by the lecturer. 6. The system introduction, testing plan, final system model, testing procedures, results, techniques comparisons and conclusions and recommended further developing need to be included at the final report. 7. The length of the Part 2 report should be between 12-20 pages. Submission Deadline Upload pdf file to Moodle site before the deadline Logbook (50% of CW) submission deadline: Friday, 24 March 2023 Formal report (50% of CW) submission deadline: Friday, 5 May 2023 DDS and EC students submission deadline: follow the university regulations 7 COMMUNICATION SYSTEMS AND WIRELESS TECHNOLOGIES CW marking scheme Part 1 Logbook for all 5 labs. (50% of CW) Part 2 Report for research experiment. (50% of CW) Assignment Grade Descriptors Critical Analysis/ Results & Discussion FIRST CLASS A++ >90% Understanding: Able to analyse critically, with arguments soundly based, and fully supported by relevant facts. Able to apply correct methods to complex problem-solving tasks and to reach an essentially complete answer. Exceptional evidence of an original or creative approach. Selection and coverage of material: Questions answered accurately and with insight, demonstrating a comprehensive knowledge of the topic and an outstanding mastery of relevant skills. Structure and presentation: Logical and well organised flow of content, clearly expressed. A complete systematic and accurate account of the assignment; exceptionally well organised and clearly presented. An outstanding record of the aims and methods of the work. Data manipulation and analysis carried out thoroughly, correctly and with evidence of originality. Critical, comparative and constructive comments on all observations, with no ‘loose ends’ (unexplained observations or unjustified claims and speculations). Considerable evidence of extended reading and original or innovative thinking. FIRST CLASS A+ 80-89% Understanding: Able to analyse critically, with arguments soundly based, and very well supported by relevant facts. Able to apply correct methods to complex problem-solving tasks and obtain a largely correct answer. Strong evidence of an original or creative approach. Selection and coverage of material: Questions answered accurately and with insight, demonstrating a thorough knowledge of the topic and a clear mastery of relevant skills. Structure and presentation: Logical and well organised flow of content, clearly expressed. A comprehensive systematic and accurate account of the assignment; exceptionally well organised and clearly presented. An excellent record of the aims and methods of the work. Data manipulation and analysis carried out thoroughly, correctly and with insight. Critical and comparative comments on all observations, with no ‘loose ends’. Considerable evidence of extended reading and some original or innovative thinking. 8 COMMUNICATION SYSTEMS AND WIRELESS TECHNOLOGIES FIRST CLASS A 70-79% Understanding: Able to analyse critically, with arguments soundly based and well supported by relevant facts. Able to apply correct methods to problem-solving tasks. Evidence of an original or creative approach. Selection and coverage of material: Questions answered accurately and with insight, demonstrating a well-informed knowledge of the topic and a mastery of relevant skills. Structure and presentation: Logical and well organised flow of content, clearly expressed. A wide-ranging systematic and accurate account of the assignment; exceptionally well organised and clearly presented. A very clear record of the aims and methods of the work. Data manipulation and analysis carried out thoroughly and correctly. Critical comments on all observations, with no ‘loose ends’. Evidence of extended reading and original or innovative thinking. UPPER SECOND CLASS B+ (65-69) B (60-64) 60–69% Understanding: Able to analyse critically, with sound arguments, supported by relevant facts. Able to apply correct methods to problem-solving tasks. Some evidence of an original or creative approach. Selection and coverage of material: Questions answered largely correctly, demonstrating an informed knowledge of the topic and good facility with the relevant skills. Structure and presentation: Logical flow of content, clearly expressed. A systematic and largely accurate account of the assignment; well organised and presented. A clear record of the aims and methods of the work. Data manipulation and analysis carried out correctly. Reasonable comments on all observations, and only a few ‘loose ends’ Evidence of some extended reading and some original or innovative thinking. LOWER SECOND CLASS C 50–59% Understanding: Attempts to analyse critically, with arguments supported by some relevant facts. Familiar with the correct methods needed for problem-solving tasks but with some difficulties in their use. Little evidence of an original or creative approach. Selection and coverage of material: Questions answered incompletely, but demonstrating some A systematic account of the assignment, reasonably presented. An adequate record of the aims and methods of the work. Data manipulation and analysis contains few inaccuracies or omissions. knowledge of the topic and some capability with the relevant skills. Structure and presentation: Logical flow of content with reasonable clarity of expression. Comments on most observations, mainly reasonable, but with several ‘loose ends’. Little evidence of extended reading or of any original or innovative thinking. THIRD CLASS D 40–49% Understanding: Some capacity to analyse critically, but arguments not always supported by relevant facts. Familiar with some of the methods needed for problem-solving tasks but unable to apply them routinely. No evidence of an original or creative approach. Selection and coverage of material: Questions answered incompletely, demonstrating a patchy knowledge of the topic and limited capability with the relevant skills. Structure and presentation: Logical flow of content but with poor clarity of expression. An unsystematic account of the assignment/task. An incomplete record of the aims and methods of the work. Data manipulation and analysis contains some inaccuracies or omissions. Few comments on the observations with many ‘loose ends’. No evidence of extended reading. FAIL F 30-39% Understanding: Some attempts to analyse critically, with unconvincing arguments unsupported by relevant facts. Familiar with only a few methods needed for problem-solving tasks but unable to apply them routinely. No evidence of an original or creative approach. Selection and coverage of material: Questions answered incompletely, demonstrating neither breadth nor depth of knowledge. Answers with key skills rarely deployed when tackling problems. Structure and presentation: Disorganised flow of content with poor clarity of expression. An unsystematic or incomplete account of the assignment. A sketchy record of the aims and methods of the work. Data manipulation and analysis contains significant inaccuracies or omissions. Very few comments on the observations with many ‘loose ends’. No evidence of further reading. 9 COMMUNICATION SYSTEMS AND WIRELESS TECHNOLOGIES FAIL F 20-29% Understanding: Limited attempts to analyse critically, with suspect arguments unsupported by relevant facts. Unfamiliar with most methods needed for problemsolving tasks and unable to apply them routinely. No evidence of an original or creative approach. Selection and coverage of material: Questions answered incompletely, demonstrating neither breadth nor depth of knowledge. Answers often irrelevant, with key skills inappropriately deployed when tackling problems. Structure and presentation: Disorganised flow of content, with poor clarity of expression. An unsystematic, incomplete and inaccurate account of the assignment. A sketchy record of the aims and methods of the work. Data manipulation and analysis contains numerous inaccuracies or omissions. Very few comments on the observations with many ‘loose ends’. No evidence of further reading. FAIL F 10-19% Understanding: Almost no attempt to analyse critically, with unsound arguments unsupported by relevant facts. Unfamiliar with basic methods needed for problem-solving tasks and unable to apply them routinely. No evidence of an original or creative approach. Selection and coverage of material: Inadequate attempt to answer the question asked with largely irrelevant or unacceptably brief material. Structure and presentation: Totally disorganised flow of content with no clarity of expression. An unsystematic, incomplete and inaccurate account of the assignment. No record of the aims and methods of the work. Almost no evidence of data manipulation and analysis. No comments on the observations. No evidence of further reading. FAIL F < 10% Understanding: No attempt to analyse critically, with no relevant arguments. No awareness of problemsolving methods. No evidence of an original or creative approach. Selection and coverage of material: No serious attempt to answer the question asked. Structure and presentation: No discernible structure. No meaningful account provided. 10 COMMUNICATION SYSTEMS AND WIRELESS TECHNOLOGIES Lab 1. Amplitude modulation in Simulink Aim Build and investigate an AM modulator with Simulink Objectives ? To understand the theoretical background of Amplitude Modulation ? To know how to build a communication model on Simulink ? To design the Simulink module of the DSBAM and analyse signal in timetable and frequency domains Theoretical background Please refer to textbook and teaching notes. Procedures You can download MATLAB to install into your home PC. https://uk.mathworks.com/academia/tah-portal/london-south-bank-university40505066.html Part 1: Build DSBAM modulator in Simulink. 1. Start Matlab, type simulink in Matlab command window. 2. Create a new Blank Model 3. Add sine wave function block from Library-Simulink-Source-Sine wave 11 COMMUNICATION SYSTEMS AND WIRELESS TECHNOLOGIES Build an AM modulator as below. You can find other blocks by search or library. Two sine wave blocks from Simulink-Source Two constant blocks , two product blocks , scop block and sum block from Simulink-Commonly Used Blocks Search “to workspace” at the search window of Library Browser Click to open and change the Variable name to “modu” 12 COMMUNICATION SYSTEMS AND WIRELESS TECHNOLOGIES You need to change the setting of the Model by Block setting: Carrier block Modulating Sig block Mod index 13 COMMUNICATION SYSTEMS AND WIRELESS TECHNOLOGIES Click to open Scope, , layout, choose three windows. Now you can run the model to study the AM waveform. You also can plot the waveform from the Matlab commond window. Plot(modu); You can enlarge the graph to check the details. Part 2: Build AM modulator and Demodulator in Simulink. Carrier 1 block could be copied from Carrier block. Search to find and add Analog Filter Design block and Mux. Now you can run the model to study the AM modulating, modulated and demodulated waveforms. Part 3: Investigate the frequency domain of DSBAM. Mux 14 COMMUNICATION SYSTEMS AND WIRELESS TECHNOLOGIES Sine Wave: DSP System Toolbox-Sources FFT: DSP System Toolbox-Transforms DSBAM: Communications Toolbox-Modulation-Analog Passband Modulation Search “spectrum” to find and add from DSP toolbox Set block as below and study on the frequency domain results. Change above sine wave frequency and carrier frequency to (10, 200), (30, 200) and (70, 200). what differences from the graph from (50, 200)? Change frequencies from (50, 100), (50, 300) and (50, 400), what are the differences between the outputs? 15 COMMUNICATION SYSTEMS AND WIRELESS TECHNOLOGIES Lab 2. Investigate FM modulation in Multisim Aim: Build FM circuit in Multisim Objectives ? To learn how to build circuit in Multisim ? To learn more about theoretical background of FM ? To investigate the bandwidth of FM signals Procedure: Part 1 build FM circuit with FM voltage source 1) Open NI Circuit Design Suite -> Multisim 2) Find the FM voltage source in the sources bin and connect it to an oscilloscope and the spectrum analyser. 3) Set the FM source to have a 100 kHz carrier with a 10 kHz modulating (Intelligence frequency) signal and a modulation index m = 5. Run this and observe the spectrum. 4) Changevalueofmand observe the effectofthisonthe sidebands amplitudes and the bandwidth. 16 COMMUNICATION SYSTEMS AND WIRELESS TECHNOLOGIES m= 1 2 3 4 5 7 8 10 12 5) Leavem=5 and change themodulating frequency.Observe the sideband spacing and the effect on thebandwidth 6) Adjust mto a value of 2.4 and observe the spectrum. What do you notice? 7) Which other value of mwill produce the same effect on the carrier? (Hint:Check the plot of theBesselfunctions below).Try this value of m– doesit behave as expected? 8) Try to make your own Bessel Function table and graph then compare with standard one. 9) Take a note of your findingsin your logbook. Part 2 build FM circuit with components (including IC chips) Try to build a FM modulator (or demodulator) with components in Multisim. 17 COMMUNICATION SYSTEMS AND WIRELESS TECHNOLOGIES Refer to examples online. https://www.multisim.com/content/r2v4TRiRU7ZHiC3AsbG5sf/fm-generation-using-555- timer/open/ https://www.multisim.com/content/ap3eywoynUYWofGkMT4UCQ/fm-modulation-anddemodulation-circuit/open/ Simple FM Demodulator Example 1. Connect the circuit as illustrated in Figure above. 2. Double-click the FM Modulator to set its parameters and set Voltage Amplitude = 20 V, Carrier Frequency = 8 MHz, Modulation Index = 5 and Signal Frequency = 10 kHz. 3. Double-click the Oscilloscope to view its display. Set the time base to 100 μs/Div and Channel A to 100 μV/Div. Select Auto triggering and DC coupling. 4. Run the simulation noting the frequency of the sine wave at the output of the detector. 5. Compare this frequency with the input modulation frequency to verify that they are the same. 6. Plot FM time versus amplitude sketch. What is the signal frequency you detected? 18 COMMUNICATION SYSTEMS AND WIRELESS TECHNOLOGIES Lab 3. BPSK and BERTool Aim Build and investigate an BPSK modulation in Simulink Objectives ? To understand the theoretical background of PSK modulation techniques ? To know how to build a BPSK model on Simulink ? To investigate the relationship between Sb/No and BER ? To know how to use BERTool to analyse SNR and BER Theoretical background Please refer to textbook and teaching notes. Procedures Part 1 Build BPSK model in Simulink Run the model with following setting on the AWGN block. 19 COMMUNICATION SYSTEMS AND WIRELESS TECHNOLOGIES Note Eb/No VS BER on logbook. Plot the graph of Eb/No vs BER. Eb/No(dB) -3 0 1 2 3 4 5 6 7 8 9 BER Part 2 Investigate BER using Bit Error Rate Analysis app Introduction: BERTool is an interactive GUI for analyzing communication systems' bit error rate (BER) performance. Using BERTool you can ? Generate BER data for a communication system using ? Plot one or more BER data sets on a single set of axes ? Fit a curve to a set of simulation data. ? Send BER data to the MATLAB workspace or to a file for any further processing you might want to perform. Procedure: 1. Start MATLAB by double-clicking the MATLAB icon 2. Type bertool at the MATLAB prompt to open the BER Analysis app. 3. Computing Theoretical BERs 20 COMMUNICATION SYSTEMS AND WIRELESS TECHNOLOGIES Go to the Theoretical tab, set the parameters to reflect the system whose performance you want to analyse, e.g. as above figure. Click Plot. 4. Compare the results you measured from Part 1 with here at BER section. 5. Change the Modulation order parameter to 4 and click Plot. 6. Plot and compare BER graph of none coding AWGN channel with modulation type and order of PSK-8, PSK-16 and PSK-32. 7. Explain and analyse your observations with the knowledge you obtain in the course. Tips: ? To recall which value of Modulation order corresponds to a given curve, click the curve. BERTool responds by adjusting the parameters in the Theoretical tab to reflect the values that correspond to that curve. ? To remove the last curve from the plot (but not from the data viewer), clear the check box in the last entry of the data viewer in the Plot column. To restore the curve to the plot, select the check box again. Workshop exercises: (a) Plot and compare BER graph of None coding, Block-Hamming coding and Block-Golay coding with PSK-2 modulation, Channel type: AWGN. (b) Plot and compare BER graph of None coding, convolutional coding soft decision and hard decision with PSK-2 modulation, Channel type: AWGN. (c) Plot and compare BER graph of QAM-4, QAM-16, QAM-64 and QAM-256, at None coding, Channel type: AWGN. (d) Set the Eb/No range 0:40 dB, PSK-2. Plot and compare BER graph of AWGN and Rayleigh (fading). Part 3: Use BERTool in conjunction with Simulink models. 21 COMMUNICATION SYSTEMS AND WIRELESS TECHNOLOGIES 1. Open BERTool and go to the Monte Carlo tab. Click Run. BERTool creates a listing in the data viewer. To fit a curve to the series of points in the BER Figure window, select the box next to Fit in the data viewer. 2. Plot BER graph for the model built in Part 1 (i) In the MATLAB Command Window, enter: EbNo = 0; me = 100; mb = 1e8; (ii) Double-clicking to open the AWGN Channel block, Set as below and click OK (iii) Open the Error Rate Calculation block. Set Target number of errors to me, set Maximum number of symbols to mb, and click OK. (iv) Double-clicking the Signal to Workspace block, set Variable name to BER, set Limit data points to last to 1, and click OK. 22 COMMUNICATION SYSTEMS AND WIRELESS TECHNOLOGIES (v) Open BERTool and go to the Monte Carlo tab. Set parameters on the Monte Carlo tab as shown in the following figure. Click Run. Results will be shown in 3 minutes. Eb/No range: 0:9; Model Name: Brower to find your saved model file completed in Part 1. 1. To compare these simulation results with theoretical results, go to the Theoretical tab in BERTool and set parameters as shown below. Click Plot. BERTool plots the theoretical curve in the BER Figure window along with the earlier simulation results. References: MATLAB Help files. 23 COMMUNICATION SYSTEMS AND WIRELESS TECHNOLOGIES Lab 4. RF Effects on Communication System Performance Transmitter IIP3 (dBm): 3rd order Input Intercept Point (IIp3): https://www.techplayon.com/physicalsignificance-iip3-important-receiver-chain/ LNA noise figure (dB): Low-noise amplifier https://en.wikipedia.org/wiki/Low-noise_amplifier https://uk.mathworks.com/help/comm/ug/impact-of-rf-effects-on-communication-systemperformance.html Open the existing model by type following in Matlab command window. openExample('comm/ImpactOfRFEffectsOnCommunicationSystemPerformanceExample') Highted blocks can be reset. Procedure: 1. Run the model at the default setting. In the default configuration, the received power spectrum below is noiseless and has no nonlinear distortions. The sidelobes of the spectrum are from the transmit and receive filter responses. The Error Rate Calculation (ERC) block computes the system BER. In the default configuration, with the ERC block discarding transient effects at the beginning of the simulation, the BER is 0. 24 COMMUNICATION SYSTEMS AND WIRELESS TECHNOLOGIES 2. Investigate multiple RF effects by using the Model Parameters block. Typical degraded value levels are shown after the '%' for each of parameters in the block mask. You can reset the following parameters in the Model Parameters block while the simulation is running: • Transmitter IIP3 • LNA noise figure • ADC number of bits • ADC full scale voltage To specify new phase noise values, stop the model first. For example, if the transmitter IIP3 is set to 15 dBm, the signal spectrum and constellation diagram show a degraded signal, and the BER degrades to approximately 2.8e-3. 3. Investigate effects of the Free Space Path Loss block. Comments on your measurements and make your conclusions. 25 COMMUNICATION SYSTEMS AND WIRELESS TECHNOLOGIES Lab 5. Build oscillators in Multisim Part 1 Colpitts Oscillator Aim: To see how the feedback components affect the performance of a BJT amplifier circuit Procedure 1. Build and simulate the oscillator as above and measure the frequency of oscillation f0, determine f0 from the theory and note any difference. If there is, what do you think might be the reason? Try to change circled emitter resistor to 3.3k?, compare the measured output frequency and waveform. 2. Note the waveforms at both ends of the feedback tank circuit and determine if they appear to match your idea of the circuit operation. 3. Determine the gain and the feedback fraction of the circuit 4. Increase C2 in 2nF steps and for each value note the frequency and the amplitude of Vf and Vout. (Note: you need to change the span of the spectrum analyser.) 5. Make C2 = 1nF again and decrease C1 in 2nF steps down to 1nF and for each value note the frequency and the amplitude of Vf and Vout Vf 26 COMMUNICATION SYSTEMS AND WIRELESS TECHNOLOGIES 6. Plot both C values against f0 and make some deduction concerning the results. 7. Plot both C values against Vf and Vout and make some deduction concerning the results. 8. Attach a spectrum analyser to the output. Note and comment on the result. 9. Build your own Colpitts Oscillator circuit and comment on the result. 27 COMMUNICATION SYSTEMS AND WIRELESS TECHNOLOGIES Part 2 The Wien-Bridge Oscillator Aim: Understanding the theory of the Wien-Bridge Oscillator (WBO) and its stabilisation Purpose This experiment investigates the deliberate use of positive feedback to create oscillation in an operational amplifier circuit. The theory behind the Wien-Bridge Oscillator is used to develop the oscillator design and predict what conditions are required to cause oscillation. The oscillator is by nature unstable and therefore requires some modification to impose a degree of stability upon it, these modifications are also explored. 1. Background theory Recall from lectures that, typically, negative feedback is used to impose stability and reduced distortion in an amplifier circuit. Therefore, in order to cause oscillation it is necessary to introduce a specific amount of positive feedback. A Wien-Bridge Oscillator (WBO) does just this and the circuit layout is given in Figure 1. The general (so-called canonical form) of a feedback system with positive or negative feedback is given by: where ?? = ? 1+?? Where A is the amplifier gain and β is the gain of the feedback network (note: is considered to provide negative feedback and hence we need to introduce a minus sign later). The loop gain is defined as the product, Aβ. The amplifier becomes an oscillator when this loop gain, Aβ = -1, hence the denominator becomes zero and the overall gain approaches infinity. In this condition, the circuit will oscillate freely without external stimulus. This property is used in the basic Wien- Bridge Oscillator as shown below in Figure 1. 2. Wien-Bridge Oscillator theory The resistor network (formed by R3, R4 and R5) determines the amplifier gain, A, of a non- inverting amplifier. Hence A = RA/RB + 1 where RA = R3 + R5(upper) and RB = R4 + R5(lower). The potentiometer has been included so that the gain can be varied a little and the motivation for this will become clear as we progress through the theory. Further, the gain of β, (the reactive section which can be considered to be inverting) can be determined from the ratio of the impedances of Z1 and Z2 asfollows: ? = − ?2 ?1 + ?2 Knowing that ?1 = 1 ??? + ? and 1 ?2 = 1 ? + ??? show that ? = − 1 3−?[ 1 ???−???] Where R1 = R2 = R and C1 = C2 = C. Oscillation will occur when the imaginary part is zero, hence ω= 1/RC. At this frequency, β will be -1/3, hence for loop gain Aβ = -1, we need A = 3. Ya Bao Page 28 Figure 1: The Wien-Bridge Oscillator. 3 Procedure 3.1 Build theWBO Using MultiSim, construct the circuit in Figure 1, remembering that the op-amp requires a dual-rail supply of ±15Volts, pins 1 and 5 (offset null) are not connected. Use the 47kΩ variable resistor to allow adjustment in the amplifier gain of the oscillator. Choose C1 and C2 to be 3.3nF and R1 = R2 = 47kΩ. Connect Vout (and ground) to the 2 channel oscilloscope and adjust the potentiometer R5 until oscillation occurs. You should notice that the oscillations are very sensitive to the gain setting, the op-amp having a tendency to saturate at the supply rails. Carefully try to adjust the potentiometer so that the oscillations are as stable as possible with a minimum of clipping. Comment on how stable the circuit is in its current form. 3.2 Check the value of the gain, A By using the value ofthe resistance on eitherside ofthe potentiometer calculateRA and RB and hence the value of the amplifier gain, A. Doesthisfigure match with theory? 3.3 Stabilising theWBO Modify your circuit to thatshown in Figure 2 below. Note here two diodes have been added in bothpolaritydirections. Notice the stabilising effectthismodificationhason thecircuit. Explain in your logbook how this works. Ya Bao Page 29 Figure 2: Stabilisation of WBO using diodes 3.4 Conclusions A stabilised Wien-Bridge Oscillator has been constructed using an op-amp and has been tested against theory. Two diodes were subsequently used to stabilise the output, preventsaturation and limit distortion. Question: The original unstable oscillator design by Max Wien in 1891 was eventually stabilised by William Hewlett in 1939. He used an incandescent bulb as a feedback resistor (effectively in place of R4). Can you explain how this worked to stabilise the output and limitthe gain? Build your own Wien-Bridge Oscillator and comment on your result. Ya Bao Page 30 Mini-Project 1. Investigate RF Satellite Link https://uk.mathworks.com/help/comm/ug/rf-satellite-link.html https://ieeexplore.ieee.org/document/7947956 at Matlab commend window, type in openExample(‘comm/RFSatelliteLinkExample’) click “commrfsatlink.slx to open Simulink model This model shows a satellite link, using the blocks from the Communications Toolbox™ to simulate the following impairments: • Memoryless nonlinearity • Free space path loss • Doppler error • Receiver thermal noise • Phase noise • In-phase and quadrature imbalances • DC offsets The model optionally corrects most of these impairments. By modelling the gains and losses on the link, this model implements link budget calculations that determine whether a downlink can be closed with a given bit error rate (BER). The gain and loss blocks, including the Free Space Path Loss block and the Receiver Thermal Noise Ya Bao Page 31 block, determine the data rate that can be supported on the link in an additive white Gaussian noise channel. Highted blocks can be reset. Exploring the Example Double-click the block labeled Model Parameters to view the parameter settings for the model. All these parameters are tunable. To make changes to the parameters as the model is running, apply them in the dialog, then update the model via ctrl+d. The parameters are: Satellite altitude (km) - Distance between the satellite and the ground station. Changing this parameter updates the Free Space Path Loss block. The default setting is 35600. Frequency (MHz) - Carrier frequency of the link. Changing this parameter updates the Free Space Path Loss block. The default setting is 4000. Transmit and receive antenna diameters (m) - The first element in the vector represents the transmit antenna diameter and is used to calculate the gain in the Tx Dish Antenna Gain block. The second element represents the receive antenna diameter and is used to calculate the gain in the Rx Dish Antenna Gain block. The default setting is [.4 .4]. Noise temperature (K) - Allows you to select from four effective receiver system noise temperatures. The selected noise temperature changes the Noise Temperature of the Receiver Thermal Noise block. The default setting is 20 K. The choices are • 0 (no noise) - Use this setting to view the other RF impairments without the perturbing effects of noise. • 20 (very low noise level) - Use this setting to view how easily a low level of noise can, when combined with other RF impairments, degrade the performance of the link. • 290 (typical noise level) - Use this setting to view how a typical quiet satellite receiver operates. • 500 (high noise level) - Use this setting to view the receiver behavior when the system noise figure is 2.4 dB and the antenna noise temperature is 290K. HPA backoff level - Allows you to select from three backoff levels. This parameter is used to determine how close the satellite high power amplifier is driven to saturation. The selected backoff is used to set the input and output gain of the Memoryless Nonlinearity block. The default setting is 30 dB (negligible nonlinearity). The choices are • 30 dB (negligible nonlinearity) - Sets the average input power to 30 decibels below the input power that causes amplifier saturation (that is, the point at which the gain curve becomes flat). This causes negligible AM-to-AM and AMto-PM conversion. AM-to-AM conversion is an indication of how the amplitude nonlinearity varies with the signal magnitude. AM-to-PM conversion is a measure of how the phase nonlinearity varies with signal magnitude. • 7 dB (moderate nonlinearity) - Sets the average input power to 7 decibels below the input power that causes amplifier saturation. This causes moderate AM-to-AM and AM-to-PM conversion, which is correctable with digital predistortion. • 1 dB (severe nonlinearity) - Sets the average input power to 1 decibel below the input power that causes amplifier saturation. This causes severe AM-to-AM and AM-to-PM conversion, and is not correctable with digital predistortion. Doppler error - Allows you to select one of two values of Doppler. The selection updates the Phase/Frequency Offset (Doppler Error) block. The default setting is 0 Hz. The choices are • 0 Hz - No Doppler on the link. • 3 Hz - Adds 3 Hz carrier frequency offset. Ya Bao Page 32 Phase noise - Allows you to select from three values of phase noise at the receiver. The selection updates the Phase Noise block. The default setting is Negligible (-100 dBc/Hz @ 100 Hz). The choices are • Negligible (-100 dBc/Hz @ 100 Hz) - Almost no phase noise. • Low (-55 dBc/Hz @ 100 Hz) - Enough phase noise to be visible in both the spectral and I/Q domains, and cause bit errors when combined with thermal noise or other RF impairments. • High (-48 dBc/Hz @ 100 Hz) - Enough phase noise to cause errors without the addition of thermal noise or other RF impairments. I/Q imbalance and DC offset - Allows you to select from five types of in-phase and quadrature imbalances at the receiver. The selection updates the I/Q Imbalance block. The default setting is None. The choices are • None - No imbalances. • Amplitude imbalance (3 dB) - Applies a 1.5 dB gain to the in-phase signal and a -1.5 dB gain to the quadrature signal. • Phase imbalance (20 deg) - Rotates the in-phase signal by 10 degrees and the quadrature signal by -10 degrees. • In-phase DC offset (1e-8) - Adds a DC offset of 1e-8 to the in-phase signal amplitude. This offset changes the received signal constellation diagram, but does not cause errors on the link unless combined with thermal noise or other RF impairments. • Quadrature DC offset (5e-8) - Adds a DC offset of 5e-8 to the quadrature signal amplitude. This offset causes errors on the link even when not combined with thermal noise or another RF impairment. This offset also causes a DC spike in the received signal spectrum. Digital predistortion - Allows you to enable or disable the Digital Predistortion subsystem. The default setting is Disabled. DC offset correction - Allows you to enable or disable the DC Blocking subsystem. The default setting is Disabled. Doppler correction - Allows you to enable or disable the Doppler Correction subsystem. The default setting is Disabled. I/Q imbalance correction - Allows you to enable or disable the I/Q Imbalance Correction subsystem. The default setting is Disabled. Results and Displays When you run this model, the following displays are active: Power Spectrum - Double-clicking this Open Scopes block enables you to view the spectrum of the modulated/filtered signal (yellow) and the received signal before demodulation (blue). Ya Bao Page 33 Comparing the two spectra allows you to view the effect of the following RF impairments: • Spectral regrowth due to HPA nonlinearities caused by the Memoryless Nonlinearity block • Thermal noise caused by the Receiver Thermal Noise block • Phase flicker (that is, 1/f noise) caused by the Phase Noise block HPA AM/AM and AM/PM - Double-clicking this Open Scopes block enables you to view the AM/AM and AM/PM conversion after the HPA. These plots enable you to view the impact that the Digital Predistortion block and HPA have on the linearity of the signal. Constellation Before and After HPA - Double-clicking this Open Scopes block enables you to compare the constellation of the transmitted signal before (yellow) and after (blue) the HPA. The amplifier gain causes the HPA Output signal to be larger than the HPA Input signal. This plot enables you to view the combined effect of both the HPA nonlinearity and digital predistortion. End to End Constellation - Double-clicking this Open Scopes block enables you to compare the reference 16-QAM constellation (red) with the received QAM constellation before demodulation (yellow). Comparing these constellation diagrams allows you to view the Ya Bao Page 34 impact of all the RF impairments on the received signal and the effectiveness of the compensations. Bit error rate (BER) display - In the lower right corner of the model is a display of the BER of the model. The BER computation can be reset manually by double-clicking the green "Doubleclick to reset BER" button. This allows you to view the impact of the parameter changes as the model is running. Experimenting with the Example This section describes some ways that you can change the model parameters to experiment with the effects of the blocks from the RF Impairments library and other blocks in the model. You can double-click the block labeled "Model Parameters" in the model and try some of the following scenarios: Link gains and losses - Change Noise temperature to 290 (typical noise level), 0 (no noise) or 500 (high noise level). Change the value of the Satellite altitude (km) or Satellite frequency (MHz) parameters to change the free space path loss. In addition, increase or decrease the Transmit and receive antenna diameters (m) parameter to increase or decrease the received signal power. You can view the changes in the received constellation in the received signal constellation diagram scope and the changes in received power in the spectrum analyzer. Raised cosine pulse shaping - Make sure Noise temperature is set to 0 (no noise). Turn on the Constellation Before and After HPA scopes. Observe that the square-root raised cosine filtering results in intersymbol interference (ISI). This results in the points being scattered loosely around ideal constellation points, which you can see in the After HPA constellation diagram. The square-root raised cosine filter in the receiver, in conjunction with the transmit filter, controls the ISI, which you can see in the received signal constellation diagram. HPA AM-to-AM conversion and AM-to-PM conversion - Change the HPA backoff level parameter to 7 dB (moderate nonlinearity) and observe the AM-to-AM and AM-toPM conversions by comparing the Transmit RRC filtered signal constellation diagram with the RRC signal after HPA constellation diagram. Note how the AM-to-AM conversion varies according to the different signal amplitudes. You can also view the effect of this conversion on the received signal in the received signal constellation diagram. In addition, you can observe the spectral regrowth in the received signal spectrum analyzer. You can also view the phase change in the received signal in the received signal constellation diagram scope. Digital predistortion With the Digital predistortion checkbox checked, change the HPA backoff level parameter to 30 dB (negligible nonlinearity), 7 dB (moderate nonlinearity), and 1 dB (severe nonlinearity) to view the effect of digital predistortion on the HPA nonlinearity. Phase noise plus AM-to-AM conversion - Set the Phase Noise parameter to High and observe the increased variance in the tangential direction in the received signal constellation Ya Bao Page 35 diagram. Also note that this level of phase noise is sufficient to cause errors in an otherwise error-free channel. DC offset and DC offset compensation - Set the I/Q imbalance and DC offset parameter to In-phase DC offset (1e-8) and view the shift of the constellation in the received signal constellation diagram. Set DC offset correction to Enabled and view the received signal constellation diagram to view how the DC offset block estimates the DC offset value and removes it from the signal. Set DC offset compensation to Disabled and change I/Q imbalance to Quadrature DC offset (5e-8). View the changes in the received signal constellation diagram for a large DC offset and the DC spike in the received signal spectrum. Note that the LNA amplifies the small DC offsets so that they are visible on the constellation diagram with much larger axis limits. Set DC offset compensation to Enabled and view the received signal constellation diagram and spectrum analyzer to see how the DC component is removed. Amplitude imbalance - With the I/Q imbalance correction disabled, set the I/Q Imbalance and DC offset parameter to Amplitude imbalance (3 dB) to view the effect of unbalanced I and Q gains in the received signal constellation diagram. Enable the I/Q imbalance correction to compensate for the amplitude imbalance. Doppler and Doppler compensation - Disable Doppler correction by unchecking the Doppler correction check box. Set Doppler error to 3 Hz to show the effect of uncorrected Doppler on the received signal constellation diagram. Enable Doppler correction to show that the carrier synchronizer restores the received constellation. Repeat the exercise with different I/Q imbalance and DC offsets. References: MATLAB Help files. Ya Bao Page 36 Mini-Project 2. Reducing the Error Rate Objective: to reduce the error rate in Channel Noise Model by using error control codes. Tools: MATLAB, Simulink, Communications Blockset. Procedure: 1. Start MATLAB by double-clicking the MATLAB icon 2. Type in simulink to open a new window. Click on the ‘Communications toolbox’, it will open all sub-libraries of communications. 3. Type channeldoc at the MATLAB prompt to open the channel noise model. Then save the model as xx_hamming in the directory where you keep your work files. (xx could be your first name) 4. Double click the BSC block , record the pre-set Error Probability in your log book. Run the model by click button on the tool bar. Compare the reading in the display block. Change the setting of Error Probability to 0.01, 0.02, 0.03, 0.05, 0.07, 0.1…, and then fix to an Error Probability of 0.07, change the Initial Seed to any other figure, compare with the reading on the displayer. Question1: what is a Binary Symmetric Channel? What is the Error Probability? What the affection make by the seed? Tip: click Help button in the BSC block. Ya Bao Page 37 5. In the Simulink Library Browser window, click Communications Blockset, → Error Detection and Correction, → Block → drag following two blocks into the model window: • Hamming Encoder block, • Hamming Decoder block 6. Click the right border of the model and drag it to the right to widen the model window. Replace each blocks by clicking and dragging. The model should now look like the following figure. 7. Insert the Hamming Encoder block between the Bernoulli Binary Generator block and the Binary Symmetric Channel block by drag it on top of the line, as shown in the following figure. So do the Hamming Decoder block between channel Block and Error Rate Calculation block. The final model should look like 8. Setting Parameters in the Hamming Code Model Ya Bao Page 38 Double-click the Bernoulli Binary Generator block and set the parameters as below. Double-click the BSC block. Set the channel error probability to 0.01, 0.02, 0.03, 0.05, 0.07, 0.1…. Compare the BER in the Display with that in step 4. Comments on your results. Compare your simulation results with the theoretical results. Question 2. Why the error rate is approximately 0.001 when the channel error is 0.01? Question 3. How to obtain a lower error rate for the same probability of error? Tips: You expect an error rate of approximately .001 for the following reason: The probability of two or more errors occurring in a codeword of length 7 is 1 – (0.99)7 – 7(0.99)6 (0.01) = 0.002 If the codeword with two or more errors are decoded randomly, you expect about half the bits in the decoded message words to be incorrect. This indicates that .001 is a reasonable value for the bit error rate. 9. Try using a Hamming code with larger parameters. To do this, change the parameters Codeword length and Message length in the Hamming Encoder and Decoder block dialog boxes. You also have to make the appropriate changes to the parameters of the Ya Bao Page 39 Bernoulli Binary Generator block. 10. Double-click the BSC block. Set the channel error probability to 0.01, 0.02, 0.03, 0.05, 0.07, 0.1…. Compare the BER in the Display with that in step 8. Comments on your results. Displaying Frame Sizes You can display the sizes of data frames in different parts of the model by selecting Signal dimensions from the Port/signal displays submenu of the Format menu at the top of the model window. This is shown in the following figure. The line leading out of the Bernoulli Binary Generator block is labelled [4x1], indicating that its output consists of column vectors of size 4. Because the Hamming Encoder block uses a [7,4] code, it converts frames of size 4 into frames of size 7, so its output is labelled [7x1]. Displaying Frame Sizes Adding a Scope to the Model To display the channel errors produced by the Binary Symmetric Channel block, add a Scope block to the model. This is a good way to see whether your model is functioning correctly. Ya Bao Page 40 The example shown in the following figure shows where to insert the Scope block into the model. To build this model from the one shown in the figure Hamming Code Model, follow these steps: Drag the following blocks from the Simulink Library Browser into the model window: Relational Operator block, from the Simulink Logic and Bit Operations library Relational Operator Set Relational Operator to ~= in the block's dialog box. The Relational Operator block compares the transmitted signal, coming from the Bernoulli Random Generator block, with the received signal, coming from the Hamming Decoder block. The block outputs a 0 when the two signals agree and a 1 when they disagree. Scope block, from the Simulink Sinks library Two copies of the Unbuffer block, from the Buffers sublibrary of the Signal Processing Blockset Signal Management library Double-click the Binary Symmetric Channel block to open its dialog box, and select Output error vector. This creates a second output port for the block, which carries the error vector. Ya Bao Page 41 Double-click the Scope block and click the Parameters button on the toolbar. Set Number of axes to 2 and click OK. Connect the blocks as shown in the preceding figure. Setting Parameters in the Expanded Model Make the following changes to the parameters for the blocks you added to the model. Error Rate Calculation Block Double-click the Error Rate Calculation block and clear the box next to Stop simulation in the block's dialog box. Scope Block The Scope block displays the channel errors and uncorrected errors. To configure the block, Double-click the block to open the scope, if it is not already open. Click the Parameters button on the toolbar. Set Time span to 5000. Click the Logging tab. Type 30000 in the Limit data points and click OK. Ya Bao Page 42 The scope should now appear as shown. To configure the axes, follow these steps: Right-click the vertical axis at the left side of the upper scope. In the context menu, select Axes properties. In the Y-min field, type -1. In the Y-max field, type 2, and click OK. Repeat the same steps for the vertical axis of the lower scope. Widen the scope window until it is roughly three times as wide as it is high. You can do this by clicking the right border of the window and dragging the border to the right, while pressing the mouse button. Observing Channel Errors with the Scope When you run the model, the Scope block displays the error data. At the end of each 5000 time steps, the scope appears as shown in the following figure. The scope then clears the displayed data and displays the next 5000 data points. Scope with Model Running Ya Bao Page 43 The upper scope shows the channel errors generated by the Binary Symmetric Channel block. The lower scope shows errors that are not corrected by channel coding. Click the Stop button on the toolbar at the top of the model window to stop the scope. To zoom in on the scope so that you can see individual errors, first click the middle magnifying glass button at the top left of the Scope window. Then click one of the lines in the lower scope. This zooms in horizontally on the line. Continue clicking the lines in the lower scope until the horizontal scale is fine enough to detect individual errors. A typical example of what you might see is shown in the figure below. Zooming In on the Scope The wider rectangular pulse in the middle of the upper scope represents two 1s. These two errors, which occur in a single codeword, are not corrected. This accounts for the uncorrected errors in the lower scope. The narrower rectangular pulse to the right of the upper scope represents a single error, which is corrected. When you are done observing the errors, select Simulation > Stop. Sending Signal and Error Data to the Workspace explains how to send the error data to the MATLAB workspace for more detailed analysis. Repeat above procedures with BCH code and RS code. Compare the results from three error control codes.