EEE/ECE 341L/342: Introduction to Communication Engineering Lab Manual PDF

Laboratory Manual Introduction to Communication Engineering Laboratory EEE/ECE 342 (V1, V2) EEE/ECE 341L (V3) Department of Electrical & Electronic Engineering (EEE) School of Engineering (SoE) Brac University Revision: July 2022 A. Course Objectives: The objectives of this course are to: - Implement the core concepts and fundamental elements of a communication system by means of hardware setup and software. - Provide students with sound understanding and knowledge of different modes of modulation schemes used in modern communication systems and basic multiplexing techniques through practical demonstration. B. Course Outcomes, CO-PO-Taxonomy Domain & Level- Delivery-Assessment Tool: Sl. CO Description POs Bloom’s Delivery Assessment taxonomy methods and tools domain/level activities EEE_ECE 341 Introduction to Communication Engineering Explain different types of modulation Cognitive/ Assignment, CO1 a Lectures, Notes and multiplexing techniques. Understand Quiz, Exam Analyze modulated and demodulated Assignment, CO2 signals in time domain and frequency b Cognitive/ Analyze Lectures, Notes Exam domain. Assignment, Apply the knowledge to solve problems CO3 a Cognitive/ Apply Lectures, Notes Quiz, Exam, related to communication engineering. Project EEE_ECE 341L / EEE_ECE 342 Introduction to Communication Engineering Lab Use hardware and software tools to Cognitive/ Apply/ Lab Work, Lab CO4 perform experiments on various e Psychomotor/ Lab Class Exam modulation schemes. Precision C. Mark Distribution Assessment Tools Weightage (%) Attendance 5 Lab Report 20 Midterm (Hardware Exam) 20 Project 25 Lab Final (Simulation Exam & Quiz) 30 D. References Sl. Title Author(s) Publication Edition Publisher ISBN 1 Modern Digital and Analog B. Lathi 2006 3rd Oxford 978-0-19- Communication Systems edition 511009-8 2 Communication Systems S. Haykin 2005 4th Wiley 978-0-47- edition 117869-9 Lab Safety and Security Issues (Please modify this part as you feel appropriate for your lab) 1. Laboratory Safety Rules (General Guidelines): The Department of EEE maintains general safety rules for laboratories. The guideline is attached in front of the door in each of the laboratories. The written rules are as follows. A. Closed shoes must be worn that will provide full coverage of the feet and appropriate personnel clothing must be worn. B. Always check if the power switch is off before plugging in to the outlet. Also, turn the instrument or equipment OFF before unplugging from the outlet. C. Before supplying power to the circuit, the connections and layouts must be checked by the teacher. D. Voltages equal or above 50V are always dangerous. Therefore, extra precautions must be taken as voltage level is increased. E. Extension cords should be used only when necessary and only on a temporary basis. F. Once the lab exercise is done, all equipment must be powered down and all probes, cords and other instruments must be returned to their proper position. G. In case of fire, disconnect the electrical mains power source if possible. H. Students must be familiar with the locations and operations of safety and emergency equipment like Emergency power off, Fire alarm switch and so on. I. Eating, drinking, chewing gum inside electrical laboratories are strictly prohibited. J. Do not use damaged cords or cords that become too hot or cords with exposed wiring and if something like that is found, inform the teacher/LTO right away. K. No laboratory equipment can be removed from their fixed places without the teacher/LTO’s authorization. L. No lab work must be performed without the laboratory teacher/lab technical officer being present. 2. Electrical Safety To prevent electrical hazards, there are symbols in front of the Electrical Distribution Board, High voltage three phase lines in the lab, Backup generator and substation. Symbols related to Arc Flash and Shock Hazard, Danger: High Voltage, Authorized personnel Only, no smoking etc. are posted in required places. Only authorized personnel are allowed to open the distribution boxes. 3. Electrical Fire: If an electrical fire occurs, try to disconnect the electrical power source, if possible. If the fire is small, you are not in immediate danger, use any type of fire extinguisher except water to extinguish the fire. When in doubt, push in the Emergency Power Off button. 4. IMPORTANT: Do not use water on an electrical fire. Lab Plan (Week-based) Serial Experiment Name Page Tentative Is this schedule experiment used for any CO assessment? Yes No Introductory Session: Discussion regarding 6 Week 1 No 1 Course material, Course Outcomes, Marks Distribution, Assessment Plan Double Sideband (DSB) AM Generation & 7-13 Week 2 Yes 2 Detection (Hardware) Single Sideband (SSB) AM Generation & 14-19 Week 3 Yes 3 Detection (Hardware) Double Sideband (DSB) and Single 20-29 Week 4 Yes Sideband (SSB) Amplitude Modulation & 4 Demodulation using MATLAB Simulink (Software) Frequency modulation by Varactor 30-34 Week 5 Yes 5 modulation and demodulation by Foster- Seeley detector (Hardware) Sampling and Signal Reconstruction 35-42 Week 6 Yes 6 (Hardware) Frequency Modulation & Demodulation and 43-48 Week 7 Yes 7 Sampling Theorem using MATLAB Simulink (Software) 8 Theory Mid Exam break Week 8 9 Amplitude Shift Keying (ASK) (Hardware) 49-56 Week 9 Yes 10 Frequency Shift Keying (FSK) (Hardware) 57-65 Week 10 Yes Digital Pass band Modulation and 66-72 Week 11 Yes 11 Demodulation (ASK, FSK, PSK) using MATLAB Simulink (Software) 12 Hardware Exam Week 12 Yes 13 Simulation Exam & Quiz Week 13 Yes 14 Project Presentation & Report Submission 73-75 Week 14 Yes Updated by: 1. Farzana Shabnam 2. Sanjida Hossain Sabah 3. Aldrin Nippon Bobby 4. Taiyeb Hasan Sakib 5. Md. Mehedi Hasan Shawon 6. Tasfin Mahmud Introductory Session: Discussion regarding Course material, Course Outcomes, Marks Distribution, Assessment Plan During the lab session of the first week the following topics should be discussed: Introducing the course materials, course outcomes, marks distribution, and assessment plan Instructions regarding group formation Lab report submission guidelines Software Installation procedures 1. Introducing the course materials, course outcomes, marks distribution, and assessment plan: The list of experiments should be provided to the students, and also an overview of the topics can be given. The course outcomes should be explained so that the students can have a clear understanding of what they are expected to learn from this course. The complete marks distribution and the assessment plan should be discussed as well. 2. Instructions regarding group formation: The following instructions could be provided to the students for the group formation purpose: a. Each group should have at most four members (exceptions can be made depending upon the available hardware facility). b. A group should be formed with the students having the same course code. c. All group members of a group should belong to the same section. 3. Lab report submission guideline: General guidelines for submitting the report could be as follows: a. Each group will submit one report per experiment b. The hard copy of the report should be submitted before the next lab session (a soft copy should also be submitted on the online platform, if necessary). c. All group members should contribute equally. If any member is not cooperating, you may remove his/her name from the lab report and send an email to the instructor informing the issue. d. Late submission will not be accepted. e. Plagiarism will be treated harshly. f. A cover page should be added with the report including the course code, course name, experiment no., experiment name, name, and ID of each of the group members. g. The report would be assessed in terms of comprehensiveness, cleanliness, and overall presentation. 6 Brac University Department of Electrical and Electronic Engineering EEE/ECE341L/342: Introduction to Communication Engineering Laboratory Experiment No: 1(a) (Hardware) Experiment Name: - Double Sideband AM Generation Objectives: 1. To investigate the generation of double sideband amplitude modulated (AM) waveforms. 2. To examine the effects of changing audio frequency and amplitude on carrier suppration. Equipment: 1) ANACOM 1/1 module 2) Power sources +12Vdc,-12Vdc. 3) Connecting wires. 4) Oscilloscope. Procedure: 1) Connect the ANACOM 1/1 module to the power supply as shown below: 2) Ensure that the following initial conditions exist on the board: a) AUDIO INPUT SELECT switch in INT position; b) MODE switch in DSB position; c) OUTPUT AMPLIFIERE’s GAIN preset in fully clockwise position; d) SPEAKER switch in OFF position. 3) Turn on power to the ANACOM 1/1 board. 4) Turn the AUDIO OSSCILATOR block’s AMPLITUDE preset to its fully clockwise (MAX) position, and examine the block’s output (t.p.14) on oscilloscope. The audio frequency is a sine wave, which will be used as a modulating signal. The modulating frequency can be varied from 300 Hz to 3.4 kHz by adjusting the AUDIO OSCILLATOR’s FREQUENCY preset. 7 5) Turn the BALANCE preset, in the BALANCE MODULATOR & BANDPASS FILTER CIRCUIT 1 block, to its fully clockwise position. 6) Monitor, in turn, in the BALANCE MODULATOR & BANDPASS FILTER CIRCUIT 1 block, at t.p. 1 and t.p. 9. 7) Next, examine the output in the BALANCE MODULATOR & BANDPASS FILTER CIRCUIT 1 block (at t.p. 3), and check that the waveforms are as shown below: The output from the BALANCED MODULATOR & BANDPASS FILTER CIRCUIT1 block (at t.p. 3) is a double- sideband AM waveform, which has been formed by amplitude-modulating the 1 MHz carrier sine wave with the audio-frequency sine wave from the audio oscillator. The frequency spectrum of this AM waveform is as shown below: 8) To determine the depth of modulation, measure the maximum amplitude (V max) and the minimum amplitude (Vmin) of the AM waveform at t.p. 3, and use the following formula: 𝑉𝑚𝑎𝑥 − 𝑉𝑚𝑖𝑛 𝑃𝑒𝑟𝑐𝑒𝑛𝑡𝑎𝑔𝑒 𝑀𝑜𝑑𝑢𝑙𝑎𝑡𝑖𝑜𝑛 = 𝑉𝑚𝑎𝑥 + 𝑉𝑚𝑖𝑛 × 100% 9) Now vary the amplitude and frequency of the audio-frequency sine wave, by adjusting the AMPLITUDE and FREQUENCY preset in the AUDIO OSCILLATOR block. The amplitude of the two sidebands can be reduced to zero by reducing the amplitude of the modulating audio signal to zero. Do this by turning the AMPLITUDE preset to its MIN position. Return the AMPLITUDE preset to its maximum position before continuing. 10) Now turn the BALANCE preset in the BALANCED MODULATOR & BANDPASS FILTER CIRCUIT 1block, until the signal at t.p. 3 is as shown below: 8 Figure 6 The BALANCE preset varies the amount of the 1 MHz carrier component, which is passed through to the modulator’s output. By adjusting the preset, until the peaks of the waveform (A, B, C and so on) have the same amplitude, we are removing the carrier component altogether. Thus the carrier has been ‘balanced out’ (or suppressed) to leave only the two sidebands. The waveform at t.p. 3 is known as the Double-Sideband Suppressed Carrier (DSBSC) waveform, and its frequency spectrum is as shown below: 11) Change the amplitude and frequency of the modulating audio signal (by adjusting the AUDIO OSCILLATOR block’s AMLITUDE and FREQUENCY presets), and note effect that these changes have on the DSBSC waveform. The amplitude of the two sidebands can be reduced to zero by reducing the amplitude of the modulating audio signal to zero. Do this by turning the AMPLITUDE preset to its MIN position, and note that the monitored signal becomes a D.C. level, including that there are now no frequency components preset. 12) Examine the output from the OUTPUT AMPLIFIER block (t.p. 13), together with the audio modulating signal (at t.p. 1), triggering the scope with the latter. Note that the DSBSC waveform appears, amplified slightly, at t.p. 13. As we will see latter, it is the OUTPUT AMPLIFIER’s output signal, which will be transmitted to the receiver. 13) By using the optional AUDIO INPUT MODULE (L.J. Order Code CT7), the human voice can be used as the modulating signal, instead of using ANACOM 1/1’s AUDIO OSCILLATOR block. 9 Brac University Department of Electrical and Electronic Engineering EEE/ECE341L/342: Introduction to Communication Engineering Laboratory Experiment No: 1(b) (Hardware) Experiment Name: - Double Sideband AM Detection Objectives: 1. To investigate the detection of double sideband amplitude modulated (AM) waveforms. 2. To examine the effects of changing audio frequency and amplitude on carrier suppuration. Equipment: 1)ANACOM 1/1 module, 1/2 module 2)Power sources +12Vdc,-12 V dc. 3)Connecting wires. 4)Oscilloscope. Procedure: 1) Position the ANACOM 1/1 and 1/2 modules, with the ANACOM 1/1 board on the left, and a gap of about three inches between them. Then connect them to the power supply as shown below: 2) Ensure that the following initial conditions exist on the ANACOM 1/1 board: a) AUDIO OSCILLATOR’s AMPLITUDE preset in fully clockwise position; b) AUDIO INPUT SELECT switch in INT position; c) BALANCE preset in BALANCED MODULATOR & BANDPASS FILTER CIRCUIT 1 block, in fully clockwise position; d) MODE switch in DSB position; e) OUTPUT AMPLIFIERE’s GAIN preset in fully counter-clockwise position; f) TX OUTPUT SELECT switch in ANT. Position; g) AUDIO AMPLIFIERE’s VOLUME preset in fully counter-clockwise position; h) SPEAKER switch in ON position. i) On-board antenna in vertical position, and fully extended. 3) Ensure that the following initial conditions exist on the ANACOM 1/1 board: a) RX INPUTSELECT switch in ANT. position; b) R.F. AMPLIFIERE’s TUNED CIRCUIT SELECT switch in INT position; c) R.F. AMPLIFIERE’s GAIN preset in fully clockwise position; d) AGC switch IN position; e) DETECTOR switch in DIODE position; f) AUDIO AMPLIFIER’s VOLUME preset in fully counter-clockwise position; g) SPEAKER switch in ON position; h) BEAT FREQUENCY OSCILLATOR switch in OFF position i) On-board antenna in vertical position, and fully extended. 10 4) Turn on power to the modules. 5) On the ANACOM 1/2 module, slowly Turn the AUDIO AMPLIFIERE's VOLUME preset clockwise, until sounds can be heard from the on-board loudspeaker. Next, turn the vernier TUNING dial until a broadcast station can be heard clearly, and adjust the VOLUME control to a comfortable level. 6) The first stage, or ‘front end’, of the ANACOM 1/2 AM Receiver is the R.F AMPLIFIER stage. This is a wide-bandwidth tuned amplifier stage, which is tuned into the wanted station by means of the TUNING dial. Once it has been tuned into the wanted station, the R.F. AMPLIFIER, having little selectivity, will not only amplify the wanted frequency, but also those frequencies which are close to the wanted frequency. As we will see later, these nearby frequencies will be removed by subsequent stages of the receiver, to leave only the wanted signal. 7) The next stage of the receiver is the MIXER stage, which mixes the R.F. AMPLIFIER’s output with the output of a LOCAL OSCILLATOR. The frequency of the LOCAL OSCILLATOR is also tuned by means of the TUNING dial, and is arranged so that its frequency is always 455Hz above the signal frequency that the R.F. AMPLIFIER is tuned to. This fixed frequency difference is always present frequency. Re-tuned the receiver to a radio station before continuing. 8) The operation of the MIXER stage is basically to shift the wanted signal down to the I.F. frequency, irrespective of the position of the TUNING dial. This is achieved in two stages : (a) by mixing the LOCAL OSCILLATOR’s output sine wave with the output from the R.F. AMPLIFIER block. This produces three frequency components : The local oscillator frequency =(fsig +IF) The sum of the original two frequencies, fsum =(2fsig + IF) The difference between the original two frequencies fdiff = (fsig + IF – fsig) = IF These three frequency components are shown below : 11 9) Note that, since the mixer’s band pass filter is not highly selective, it will not completely remove the LOCAL OSCILLATOR and SUM frequency components from the mixer’s output. This is the case particularly with the LOCAL OSCILLATOR component, which is much larger in amplitude than the SUM and DIFFERENCE components. 10) Tune in to a strong broadcast station again, and note that the monitored signal shows little, if any, sign of modulation. This is because the wanted component, which is now at the I. F. frequency of 455kHz, is still very small in comparison to the LOCAL OSCILLATOR component. 11) Examine the output of I. F. AMPLIFIER 2 (t.p.28) with an a.c.-coupled oscilloscope channel, noting that the amplitude of the signal has been further amplified by this second I.F. amplifier stage. 12) The next step is tc extract this audio information from the amplitude variations of the signal at the output of I.F. AMPLIFIER 2 (at t.p.28). 13) The final stage of the receiver is the AUDIO AMPLIFIER block. The block contains a simple low-pass filter which passes only audio frequencies., and remove the high frequency ripple from the DIODE DETECTOR’s output signal. This filtered audio signal is applied to the input of an audio power amplifier, which drives the onboard loudspeaker. The final result is the sound you are listening to! 14) Now that we have examined the basic principles of operation of the ANACOM ½ receiver for the reception and demodulation of AM broadcast signals, we will try receiving the A.M. signal from the ANACOM 1/1 Transmitter. 15) On the ANACOM 1/1 module, turn the VOLUME preset clockwise, until you can hear the tone of the AUDIO OSCILLATOR’s output signal, from the on-board loudspeaker. 16) On the ANACOM ½ Receiver, adjust the VOLUME preset so that the receiver’s output can be clearly heard. Then adjust the receiver’s TUNING dial until the tone generated at the Transmitter is also clearly audible at the Receiver and adjust the Receiver’s VOLUME preset until the tone is at a comfortable level. 17) We will now investigate the operation of the Receiver’s AGC CIRCUIT. The AGC CIRCUIT prevents the receiver from overloading when it is tuned into a strong A.M. broadcast signal, by monitoring the d.c. bias voltage at the output of the DIODE DETECTOR. 12 18) The receiver’s AGC CIRCUIT is currently in operation. To examine its behavior, monitor the output of I.F. AMPLIFIER 2, together with the output of the DIODE DETECTOR. 19) We will prevent the AGC CIRCUIT from controlling the gain of the receiver, by disconnecting it from the R.F. AMPLIFIER and I.F. AMPLIFIER 1 blocks. Do this by putting the receiver’s AGC switch in the OUT position, and note the effect on the two monitored waveforms. 20) By using the optional AUDIO INPUT MODULE, the human voice can be used as the transmitter’s audio modulating signal, instead of using ANACOM 1/1’s AUDIO OSCILLATOR block. 13 Brac University Department of Electrical and Electronic Engineering EEE/ECE341L/342: Introduction to Communication Engineering Laboratory Experiment No: 2(a) (Hardware) Experiment Name:- Single Sideband AM Generation Objective: 1) To investigate the generation of single sideband amplitude modulated (AM) waveforms. 2) To examine the effects of changing audio frequency and amplitude on carrier suppuration. Equipment: 1) ANACOM 1/1 module 2) Power sources +12Vdc,-12Vdc. 3) Connecting wires. 4) Oscilloscope. Procedure: 1) Connect the ANACOM 1/1 module to the power supply as shown below: 2) Ensure that the following initial conditions exist on the board: a) AUDIO INPUT SELECT switch in INT position; b) MODE switch in SSB position; c) OUTPUT AMPLIFIER’s GAIN preset in fully clockwise position; d) SPEAKER switch in OFF position. 3) Turn on power to the ANACOM 1/1 board. 4) Turn the AUDIO OSSCILATOR block’s AMPLITUDE preset to its fully clockwise (MAX) position, and examine the block’s output (t.p.14) on oscilloscope. The audio frequency is a sine wave, which will be used as a modulating signal. The modulating frequency can be varied from 300Hz to 3.4KHz by adjusting the AUDIO OSCILLATOR’s FREQUENCY preset. 14 5) Turn the BALANCE preset, in the BALANCE MODULATOR & BANDPASS FILTER CIRCUIT 1 block, to its fully clockwise position. 6) Monitor, in turn, in the BALANCE MODULATOR & BANDPASS FILTER CIRCUIT 2 block, at t.p.15 and t.p.6. 7) Next, examine the output of the , in the BALANCE MODULATOR & BANDPASS FILTER CIRCUIT 1 block (at t.p.3), and check that the wave forms are as shown below: 8) The DSBSC output from the BALANCE MODULATOR block is next passed on to the CERAMIC BANDPASS FILTER block, whose purpose is to pass the upper sideband, but block the lower sideband. This is shown in the frequency spectrum below : 9) Monitor the output of the CERAMIC BANDPASS FILTER block (at t.p.20), together with audio modulating signal (at t.p.15), using the latter signal to trigger the oscilloscope. Note that the envelope of the signal at t.p. 20 now has fairly constant amplitude, as shown below : 15 10) Now trigger the oscilloscope with the CERAMIC BANDPASS FILTER’s output signal (t.p.20) and note that the signal is a good, clean sine wave, indicating that the filter has passed the upper only. 11) Note that there is some variation in the amplitude of the signal at the filter’s output (t.p.20) as the modulating frequency is changed. This variation is due to the frequency response of the CERAMIC BANDPASS FILTER and is best explained by considering the spectrum of the filter’s input signal at the MIN and MAX positions of the FREQUENCY preset. 12) Note that , by passing only the upper sideband (of frequency (fc +fm)), all we have actually done is to shift our audio modulating signal (of frequency fm) up in frequency by an amount equal to the carrier frequency fc. 13) With the AUDIO OSCILLOSCOPE block’s FREQUENCY preset roughly in this midway position, turn the block’s AMPLITUDE preset to its MIN position, and note that the amplitude of the signal at the CERAMIC BANDPASS FILTER’s output (t.p.20) drops to zero. 14) You will recall that we have used a CERAMIC BANSPASS FILTER to pass the wanted upper sideband, but reject the unwanted lower sideband which was also produced by the amplitude modulation process. We used this type of filter because it passes the upper sideband, yet has a sufficiently sharp response to strongly attenuate the lower sideband, which is close by. 15) Now examine the output of the BALANCED MODULATOR & BANDPASS FILTER CIRCUIT 2 block (at t.p. 22) and check that waveform is a good sine wave of frequency approximately 1.455MHz. 16) Monitor the 1.455MHz SSB signal (at t.p.22), together with the audio modulating signal (at t.p.15), triggering the scope with the latter. 17) Examine the final SSB output (at t.p. 22) together with the output from the OUTPUT AMPLIFIER block (t.p.13). As we will see later, it is the OUTPUT AMPLIFIER’s output signal which will be transmitted to the receiver. 18) By using the optional AUDIO INPUT MODULE, the human voice can be used as the audio modulating signal, instead of using ANACOM 1/1’s AUDIO OSCILLATOR block. 16 Brac University Department of Electrical and Electronic Engineering EEE/ECE341L/342: Introduction to Communication Engineering Laboratory Experiment No: 2(b) (Hardware) Experiment Name:- Single Sideband AM Detection Objective: 1) To investigate the detection of single sideband amplitude modulated (AM) waveforms. 2) To examine the effects of changing audio frequency and amplitude on carrier suppuration. Equipment: 1) ANACOM 1/1 module, 1/2 module. 2) Power sources +12Vdc,-12Vdc. 3) Connecting wires. 4) Oscilloscope. Procedure: 1) Position the ANACOM 1/1 and 1/2 modules, with the ANACOM 1/1 board on the left, and a gap of about three inches between them. Then connect them to the power supply as shown below: 2) Ensure that the following initial conditions exist on the ANACOM 1/1 board: a) AUDIO OSCILLATOR’s AMPLITUDE preset in fully clockwise position; b) AUDIO INPUT SELECT switch in INT position; c) MODE switch in SSB position; d) OUTPUT AMPLIFIERE’s GAIN preset in fully counter-clockwise position; e) TX OUTPUT SELECT switch in ANT. Position; f) AUDIO AMPLIFIERE’s VOLUME preset in fully counter-clockwise position; g) SPEAKER switch in ON position. h) On-board antenna in vertical position, and fully extended. 3) Ensure that the following initial conditions exist on the ANACOM 1/1 board: a) RX INPUTSELECT switch in ANT. position; 17 b) R.F. AMPLIFIERE’s TUNED CIRCUIT SELECT switch in INT position; c) R.F. AMPLIFIERE’s GAIN preset in fully clockwise position; d) AGC switch IN position; e) DETECTOR switch in PRODUCT position; f) AUDIO AMPLIFIER’s VOLUME preset in fully counter-clockwise position; g) SPEAKER switch in ON position; h) BEAT FREQUENCY OSCILLATOR switch in ON position i) On-board antenna in vertical position, and fully extended. 4) Turn on power to the modules. 5) On the ANACOM 1/1 module, examine the Transmitter’s output signal (t.p. 13), and make sure that this is a good SSB waveform, by checking that the signal is a reasonably good sine wave for all positions of the AUDIO OSCILLATOR’s FREQUENCY preset. 6) Turn ANACOM 1/1’s AMPLITUDE preset to its fully counter -clockwise position and note that the amplitude of the monitored output signal from ANACOM 1/1 (at t.p. 13) drops to zero. This illustrates that the SSB waveform contains no carrier – if the amplitude of the modulating audio signal drops to zero, so does the amplitude of the transmitted SSB signal. 7) We will now transmit the SSB waveform to the ANACOM 1/2 Receiver. Since ANACOM 1/1’s TX OUTPUT SELECT switch is in the ANT. Position, the SSB signal at t.p.13 is fed to the transmitter’s antenna. Prove this by touching ANACOM 1/1’s antenna and noting that the loading caused by your hand reduces the amplitude of the SSB waveform at t.p.13. 8) On the ANACOM 1/2 module, monitor the output of the I.F. AMPLIFIER 2 block (t.p.28) and turn the TUNNING dial until the amplitude of the monitored signal is at its greatest. This should occur at about 85-95 on the TUNNING dial. 9) Since the incoming SSB signal contains no carrier component, the Receiver’s AGC CIRCUIT cannot make use of incoming carrier amplitude, in order to control the Receiver’s gain. 10) For SSB reception, the following blocks of the Receiver operate in the same way as they did for the reception of Double-sideband AM signals: R.F AMPLIFIER LOCAL OSCILLATOR MIXER I.F. AMPLIFIER 1 I.F. AMPLIFIER 2 11) The receiver’s BEAT FREQUENCY OSCILLATOR (BFO) produces a sine wave at the I.F. frequency of 455kHz. This 455kHz sine wave is input to the Receiver’s PRODUCT DETECTOR block, where it is mixed with the SSB signal from I.F. AMPLIFIER 2. 12) Monitor the output of ANACOM ½’s BEAT FREQUENCY OSCILLATOR block (t.p.46) and note that this carries a sine wave of 455kHz. On the ANACOM 1/2 Receiver, adjust the VOLUME preset so that the receiver’s output is clearly audible. 13) On the ANACOM 1/1 module, turn the VOLUME preset clockwise, until you can hear the tone of the AUDIO OSCILLATOR’s output signal, in addition to the tone from the ANACOM 1/2 board. 18 14) On the ANACOM 1/2 module, monitor the output of the PRODUCT DETECTOR block (at t.p.37), together with the output of the AUDIO AMPLIFIER block (t.p.39), triggering the ‘scope with the latter signal. Vary the frequency of the Transmitter’s audio modulating signal by adjusting the AUDIO OSCILLATOR’s FREQUENCY preset on the ANACOM 1/1 module. 15) With the Receiver’s TUNNING dial adjusted for correct demodulation of the transmitted SSB signal, you may notice that there is a slight drift in the tone generated by the Receiver. This is due to small frequency drifts in the Transmitter and receiver oscillator circuits, leading to changes in the difference frequency produced by the PRODUCT DETECTOR. 16) In practice, it would not be possible to align the Receiver to the Transmitter by comparing tones, since the Receiver’s operator would not have access to the original audio modulating signal. Brac University 19 Department of Electrical and Electronic Engineering EEE/ECE341L/342: Introduction to Communication Engineering Laboratory Experiment No: 1 (Software) Experiment Name:- Double Sideband Amplitude Modulation & Demodulation 1. Objective: To perform the DSBAM and DSBSC signal Generation and Detection. 2. Theoretical Background: Fundamentals of Analog Communications: Amplitude Modulation: Mathematical Expressions: 20 Amax and Amin are the maximum and minimum amplitudes of the modulated wave. 3. Problem Statement: Draw all the models one-by-one in the MATLAB Simulink window. Set the simulation time from the model window as below: SimulationàSimulation parameters: Start time = 0.0 & Stop time = 10.0. Then simulate all the models and observe all the wave shapes at different points of the model. 4. Software and Device requirement: MATLAB (with simulink) Minimum PC specifications: Windows/ Mac: Microsoft® Windows® 7 Professional, Enterprise, Ultimate or Home Premium (64-bit); Windows 8 (64-bit) (All Service Packs); Windows 10 (64-bit); Windows 2008 R2 Server; Windows 2012 Server (All Service Packs). Ram: 2 GB Processor: Intel® Pentium® 4 or AMD Athlon XP 2000 with multi-core CPU Display resolutions: 1,024 x 768 display resolution with true color (16-bit color) 5. Procedure 21 You can take the blocks from the Simulink Library Browser. Blocks to be used for this experiment: The blocks that you will use in this experiment can be taken from the following mentioned library: Bernoulli Binary Generator: Communication Blockset➜Comm sources➜Data Sources➜Bernoulli Binary Generator Sine Wave: Simulink Sources➜Sine wave Product: Simulink➜Math operations➜Product AWGN Channel: Communication Block Set➜Channels➜AWGN Channel Digital Filter Design: Communication Blockset➜Comm Filters➜Filter Designs Library Link➜Digital Filter Design Analog/Digital Filter Design: Signal Processing Blockset➜Filtering➜Filter Implementations➜Analog/Digital Filter Design Spectrum Scope: Signal Processing Blockset ➜Signal Processing Sinks➜Spectrum Scope Compare to Constant: Simulink➜Logic & Bit Operations➜Compare to Constant Scope: Simulink➜Sinks➜Scope Constant: Simulinks➜Sources➜Constants Abs: Simulink➜Math operations➜Abs Sum: Simulink➜Math Operations➜Sum Parameters to be used for different blocks: Spectrum Scope: ○ Check ‘Show Scope Properties’ & ‘Buffer input’. Set: Buffer size: 128, Buffer overlap: 64 & Number of spectral averages: 2. ○ Check ‘Show axis properties’. Set: Frequency unit: Hertz & Frequency range: [-Fs/2…Fs/2]. ○ After Simulation you will observe a window for each spectrum scope. To view the spectrum more clearly, set AxesàAutoscale from the spectrum window. 22 Sine wave: ○ Both modulator & demodulator: Sine type: Time based Amplitude: 1.0 Frequency: 2*pi*1 rad/sec Sample time: 1/1000 For carrier signal: Sine type: Time based Amplitude: 2.0 Frequency: 2*pi*20 rad/sec Sample time: 1/1000 Product: Number of inputs: 2 & Multiplication: Element wise AWGN Channel: Initial seed: 67, Mode: Variance from mask & variance: 1. Note: You can vary the noise power by varying variance Digital Filter Design: Filter type: Lowpass Design method: FIRàEquiripple Filter order: Minimum order Frequency Specifications: Units: Hz, FS: 5000, Fpass=5, Fstop=8. Magnitude Specifications: Units: dB, Apass=1, Astop=80. Then click Design Filter. The magnitude response of the filter will be changed according to your specifications. Note: You should choose your Fpass and Fstop frequencies depending on the frequency of your modulating signal. Compare to constant: Operator: >=. Constant: Depends on your system. This is the threshold value of the detector. Scope: Data History: Uncheck the ‘Limit data points to last’. Constant: Constant value: 1 Abs: Check the ‘saturate on integer overflow’ & ‘Enable zero crossing detection’. Sum: List of signs: |+- (subtraction will be done). Note: To sum up two inputs, list of signs: |++ 23 Simulation Model 6. Report: I. Add AWGN channel (to see the effect of noise) in between your modulator and demodulator and observe the output. Include your model diagram and output waveforms (choose different modulation index value for under, over & perfect modulation) in the report. II. Build the following block of Balanced Modulator to generate DSBSC waveform in MATLAB Simulink. Observe the modulated output. Also demodulate (Synchronous Demodulation) the DSBSC output to extract the message signal. 24 Brac University Department of Electrical and Electronic Engineering EEE/ECE341L/342: Introduction to Communication Engineering Laboratory Experiment No: 2 (Software) Experiment Name:- Amplitude Modulation (AM) Single Sideband Suppressed Carrier (SSB- SC)- Modulation and Demodulation 1. Objective: To perform the AM SSB-SC signal Generation and Detection. 2. Theoretical Background: Advantages of SSB-SC AM: DSB wastes Bandwidth: If bandwidth of message is B (in Hz), then bandwidth of ψDSB signal is 2B (in Hz) and Bandwidth is an important constraint in today’s congested spectrum Solution: Use ψSSB signal, that has bandwidth B in Hz SSBSC: One sideband→ BW reduction DSBSC: No carrier → reduction of power by 50% SSBSC: Only one sideband → reduction of power by 50% more Mathematical Expressions: Let, the modulating signal be, m(t) and the carrier signal be 𝑐𝑜𝑠𝜔𝑐 (𝑡) SSB modulated output: where 𝑚ℎ (t) = Hilbert Transform of m(t) = -π/2 phase-shifted version of m(t) Multiply by carrier for demodulation: Then use LPF to extract message signal 25 SSB Modulation- SSB Demodulation- 3. Problem Statement: - Draw all the models one-by-one in the MATLAB Simulink window. - Set the simulation time from the model window as below: Simulation---->Simulation parameters: Start time = 0.0 & Stop time = 10.0. - Then simulate all the models and observe all the wave shapes at different points of the model. 4. Software and Device requirement: MATLAB (with simulink) Minimum PC specifications: Windows/ Mac: Microsoft® Windows® 7 Professional, Enterprise, Ultimate or Home Premium (64-bit); Windows 8 (64-bit) (All Service Packs); Windows 10 (64-bit); Windows 2008 R2 Server; Windows 2012 Server (All Service Packs). Ram: 2 GB Processor: Intel® Pentium® 4 or AMD Athlon XP 2000 with multi-core CPU Display resolutions: 1,024 x 768 display resolution with true color (16-bit color) 26 5. Procedure: You can take the blocks from the Simulink Library Browser. The blocks that you will use in this experiment can be taken from the following mentioned library: (i) Bernoulli Binary Generator: Communication Blockset--> Comm sources--> Data Sources--> Bernoulli Binary Generator (ii) Sine Wave: Simulink--> Sources-->Sine wave (iii) Product: Simulink-->Math operations-->Product (iv) AWGN Channel: Communication Block Set-->Channels-->AWGN Channel (v) Digital Filter Design: Communication Blockset-->Comm Filters-->Filter Designs Library Link-->Digital Filter Design (vi) Analog/Digital Filter Design: Signal Processing Blockset-->Filtering-->Filter Implementations -->Analog/Digital Filter Design (vii) Spectrum Scope: Signal Processing Blockset-->Signal Processing Sinks-->Spectrum Scope (viii) Compare to Constant: Simulink-->Logic & Bit Operations-->Compare to Constant (ix) Scope: Simulink-->Sinks-->Scope (x) Constant: Simulinks-->Sources-->Constants (xi) Abs: Simulink-->Math operations-->Abs (xii) Sum: Simulink-->Math Operations-->Sum Parameters to be used for different blocks: Spectrum Scope: Check ‘Show Scope Properties’ & ‘Buffer input’. Set: Buffer size: 128, Buffer overlap: 64 & Number of spectral averages: 2. Check ‘Show axis properties’. Set: Frequency unit: Hertz & Frequency range: [-Fs/2…Fs/2]. After Simulation you will observe a window for each spectrum scope. To view the spectrum more clearly, set Axes-->Autoscale from the spectrum window. Sine wave: Both modulator & demodulator: Sine type: Time based 27 Amplitude: 1.0 Frequency: 2*pi*1 rad/sec Sample time: 1/1000 For carrier signal: Sine type: Time based Amplitude: 2.0 Frequency: 2*pi*20 rad/sec Sample time: 1/1000 Product: Number of inputs: 2 & Multiplication: Element wise AWGN Channel: Initial seed: 67, Mode: Variance from mask & variance: 1. Digital Filter Design: Filter type: Lowpass Design method: FIRE-->Equiripple Filter order: Minimum order Frequency Specifications: Units: Hz, FS: 5000, Fpass=5, Fstop=8. Magnitude Specifications: Units: dB, Apass=1, Astop=80. Then click Design Filter. The magnitude response of the filter will be changed according to your specifications. Note: You should choose your Fpass and Fstop frequencies depending on the frequency of your modulating signal. Compare to constant: Operator: >=. Constant: Depends on your system. This is the threshold value of the detector. Scope: Data History: Uncheck the ‘Limit data points to last. Constant: Constant value: 1 Abs: Check the ‘saturate on integer overflow’ & ‘Enable zero crossing detection. Sum: List of signs: |+- (subtraction will be done). Note: To sum up two inputs, list of signs: |++ 28 Simulation Model: 6. Lab Report: 1. Add AWGN channel (to see the effect of noise) in between your modulator and demodulator and observe the output. Include your model diagram and output waveforms (USB, LSB and demodulated waveforms) in the report. 2. Use the built in SSBAM modulator and demodulator from the library and do the simulation. Include your model diagram and output waveforms (Modulated and demodulated waveforms) in the report. Additional Task: (Optional) Use a spectrum analyzer from the library and show the USB, LSB and extracted output in frequency domain. [Hint: Spectrum Analyzer settings: Type: RMS, Trace option-->Scale-->Linear] 29 Brac University Department of Electrical and Electronic Engineering EEE/ECE341L/342: Introduction to Communication Engineering Laboratory Experiment no: 3 (Hardware) Experiment Name: - Frequency modulation by Varactor modulation and demodulation by Foster-Seeley detector Objective: 1) Demonstration of frequency modulation by Varactor modulator. 2) Demonstration of frequency demodulation by Foster-Seeley detector and effect of noise on its performance. Equipment: 1) Anacom-2 module. 2) Power supply 3) Oscilloscope 4) Frequency meter 5) Procedure: Part A: Frequency modulation by Varactor modulator: 1) Connect the Anacom-2 module to the appropriate power supply. 2) Ensure that the following initial conditions exists on the Anacom-2 module: a) All switched faults OFF. b) AMPLITUDE preset (in the MIXER/AMPLIFIER block) in fully clockwise position. c) VCO switch (in PLL block) in OFF position. 3) Turn on power to the ANACOM2 module. 4) Turn the AMPLITUDE PRESET (in the AUDIO OSCILATOR block) in fully clockwise (Max.) position and observe its output (at t.p 1) on oscilloscope. This is the modulating signal whose frequency (300 Hz to 3400 Hz) and amplitude can be varied by FREQUENCY PRESET and AMPLITUDE PRESET on the block. Leave the AMPLITUDE PRESET in fully counter clockwise (Min.) position for the time being. 5) Link the AUDIO OSCILLATOR output to the AUDIO INPUT of the MODULATOR CIRCUIT as shown in Fig. 3 and put the VARACTOR/VARACTOR switch in the VARACTOR position. 6) As like AUDIO block the amplitude of the FM carrier can be adjusted by the AMPLITUDE preset on the MIXER/AMPLIFIER block and the frequency (451 kHz to 458 kHz) can be varied by the CARRIER FREQUENCY preset on the VARACTOR MODULATOR block. 30 In the VARACTOR MODULATOR block put the CARRIER FREQUENCY preset in its midway position and AMPLITUDE preset in fully clockwise position. Monitor the signal at t.p.34. It is the unmodulated carriers as the amplitude of the modulating signal is zero. 7) Turn the CARRIER FREQUENCY preset to its fully counter clockwise position-this corresponds to minimum base bias voltage. Monitor signal at t.p.34 (Oscillator output) and at t.p.21 (base bias voltage). Now slowly turn the CARRIER FREQUENCY preset clockwise and record the oscillator frequency (with a frequency meter at t.p.34) for each 0.1 Volts intervals of the base voltage. Plot the oscillator frequency Vs base bias voltage as shown in Fig.1. 8) If it is possible to change the base bias voltage with sinusoidal modulating signal a sinusoidal change in oscillator frequency can be obtained. Thus frequency modulation is performed with a VARACTOR modulator. 9) Now keeping the CARRIER FREQUENCY preset in fully CCW position observe the FM output at t.p.34. Now turn AMPLITUDE preset (in AUDIO OSCILLATOR block) to its fully clockwise position and note what happens to the FM output. Decrease amplitude of the modulating signal by turning AMPLITUDE preset (in AUDIO OSCILLATOR block) slowly CCW and observe the frequency deviation in the FM output. 10) Return the AMPLITUDE preset (in AUDIO OSCILLATOR block) to its fully CW position. Vary the frequency of the modulating signal by adjusting the FREQUENCY preset (in AUDIO OSCILLATOR block) and observe whether the FM output pattern changes or not. The change in AUDIO OSCILLATOR frequency does not effect the amount of frequency deviation-it actually determines how many times per second the carrier deviates from its center position. But Oscilloscope can not show the rate of change of frequency deviation and for this reason it appears that the AUDIO OSCILLATOR frequency have no effect. Now turn the CARRIER FREQUENCY preset slowly CW and observes the frequency deviation. 31 Part B: Frequency demodulation by Foster-Seeley detector: 1) Connect a signal generator having a sinusoidal output of amplitude 1V(p-p) and frequency 400 kHz to the INPUT socket of FOSTER-SEELEY DETECTOR block. 2) Now vary the frequency of the signal generator from about 430 kHz to 480kHz in 5 kHz steps and record the DC voltage at t.p.52 with the help of a multimeter for each step. Now plot the DC level against frequency. The curve should look like as shown in Fig.2: 3) Now disconnect the signal generator. Adjust CARRIER FREQUENCY preset (in the VARACTOR MODULATOR block) to have carrier frequency of 450 kHz. Now modulate this carrier with a signal from the AUDIO OSCILLATOR and apply this modulated signal to the input of the FOSTER-SEELEY block as shown in Fig.3. 4) Now monitor the output of FOSTER-SEELEY block (at t.p.52) along with input audio signal (at t.p.14) at dual mode and compare the two signals. The signal should contain two components: a) A sine wave at the same frequency as the audio signal at t.p.14. b) A high frequency ripple component of small amplitude. 5) To remove the high frequency ripple apply the signal at t.p.52 to the LOW PASS FILTER/AMPLIFIER block. Now observe the signal at the output of the LOW PASS FILTER at t.p.73. 6) We will now investigate the effect of noise on the system. For this put the AMPLITUDE preset in its MAX position and the FREQUENCY preset in its MIN position in the AUDIO OSCILLATOR block. Adjust the signal 32 generator for a sinusoidal output of amplitude 100 mV (p-p), and frequency 2kHz, which will be used as noise input. Connect this signal to the NOISE INPUT socket in ANACOM2’s MODULATOR CIRCUIT block and monitor the noise input (at t.p.5) and the FM output (at t.p.34). The FM signal will be amplitude modulated by the ‘noise’ input in addition to be frequency modulated by the audio input. 7) Monitor the audio modulating signal (at t.p.14) and the output of the LOW PASS FILTER block (at t.p.73). A considerable amount of ‘ripple’ may be seen (at t.p.73) at the frequency of the ‘noise’ input. This is because the FOSTER-SEELEY DETECTOR is sensitive to amplitude variations in the incoming FM signal. 8) To reduce the amplitude variation connect the AMPLITUDE LIMITER as shown in Fig.4 and observe the signal at AMPLITUDE LIMITER output (at t.p.68) and at LOW PASS FILTER output (at t.p.73). Compare the final output with and without AMPLITUDE LIMITER. Report: 1) Describe the principle of operation of the VARACTOR MODULATOR and the FOSTER-SEELEY DETECTOR. 2) Show all the observations with necessary wave shapes in your report and describe them. 33 34 Brac University Department of Electrical and Electronic Engineering EEE/ECE341L/342: Introduction to Communication Engineering Laboratory Experiment No: 4 (Hardware) Experiment Name: - Sampling and Signal Reconstruction Performance Objectives: A) Investigate methods used to sample a signal and to recognize the signal that results from each method. B) Investigate a method used to reconstruct the intelligence from a sampled signal and demonstrate how the sampling signal frequency and the low pass filter characteristic affect reconstruction. Equipment and Materials: 1) MODICOM 1 module 2) Oscilloscope 3) Power sources +12Vdc,-12Vdc. 4) Connecting wires. Basic Concept: 1) Sampling is a method used in pulse modulation to identify the intelligence signal by a sequence of pulses that represents the intelligence signal by a sequence of pulses that represents the intelligence at a particular time. 2) Natural sampling is a type of sampled signal in which the to of each sample pulse follows the intelligence signal during the pulse-width time of the sampling signal. 3) Flat-topped sampling is a type of sampled signal in which the to of each sample pulse represents a signal level of intelligence during the pulse-width time of the sampling signal. 4) The sampling principle states that the intelligence can be reconstructed by filtering when the sampling signal frequency or sampling (Fs) is greater than twice the maximum intelligence signal frequency (Fm). 5) The Nyquist rate is a condition that occurs when the sampling signal frequency is equal to twice the maximum intelligence signal frequency (Fs = 2Fm, where Fs is the sampling signal frequency and Fm is the maximum frequency of the intelligence signal). 6) The frequency response of the low-pass filter must be capable of passing the maximum intelligence signal to reconstruct the intelligence signal frequency while rejecting side band frequencies of the sampling signal to reconstruct the intelligence free of distortion. 35 FEATURES Separate SAMPLE and SAMPLE/HOLD outputs. SECOND ORDER and FOURTH ORDER low pass f filters. On-board synchronized 1kHz sine wave. Five switch selectable sampling frequencies. Sampling duty cycle variable in discrete steps. OUTLINE OF THE BOARD The purpose of the MODICOM 1 board is to illustrate how a signal may be sampled, transmitted as a series of samples, and reconstructed at the receiver by low pass filtering. A layout diagram for the board is shown overleaf. The board contains two low pass filters (each with a cut-off frequency of 3.4 kHz): a second-order filter with a roll-off slope of -12dB/octave, and a fourth-order filter with a sharper roll-off slope of -24dB/octave. Sampling frequencies of 2 kHz, 4kHz, 8kHz, 16kHz, and 32kHz can be selected, and the sampling duty cycle can be varied in 1O steps from 03 to 90. These features enable the student to examine the effect of different sampling frequencies and sampling duty cycles on the reconstructed waveform. The transmitter provides a SAMPLE/HOLD output in addition to a SAMPLE output so that comparisons can be drawn concerning the suitability of the two types of the waveform as far as signal reconstruction is concerned. Although an external analog input may be used by the student, a unique feature is the onboard 1 kHz sine wave, this is synchronized to the sampling waveform and allows a 'static' oscilloscope display to be observed. Finally, the user has the option of supplying an external sampling control signal, to experiment with other sampling frequencies and duty cycles. 36 37 Procedure: 1. Connect supplies to board. The d.c. Power requirements are; +5V, 1A, ±12V @ 1 A/rai l. 2. Ensure SAMPLING CONTROL switch is in 'INTERNAL' position. 3. Put DUTY CYCLE SELECTOR switch in position 'S'. 4. Link 1 kHz sine wave output to ANALOG INPUT. 5. Turn on the power to the board. 6. Display 1 kHz sine wave (t.p.7) and SAMPLE OUTPUT (t.p.33) on an Oscilloscope. This shows the 1 kHz sine wave being sampled at 321 kHz, so there are 32 samples for every cycle of the sine wave (see Fig.1 at the end of this chapter). 7. Link SAMPLE OUTPUT to the input of FOURTH ORDER LOW PASS Fi TER. Display SAMPLE OUTPUT ( t.p. 33) and the output of the FOURTH ORDER LOW PASS FILTER (t.p.49) on the oscilloscope, to show how the original 1KHz sine wave can be reconstructed from the samples by low pass f filtering CF ig.2). 8. By successive presses of the FREQUENCY SELECTOR switch, change the sampling frequency to 2kHz, 41KHz, 8kHz, I61kHz, and back to 321KHz (Sampling frequency is always 1/ 10 of the frequency indicated by the Illuminated LED). Observe how the SAMPLE OUTPUT changes in each case, and how the lower sampling rates introduce distortion into the filter's output waveform.The sampled waveform contains components at fx, fs-fx, and fs+rx, 2fs-fx, etc., where fx = input sine wave frequency, fs = sampling frequency. Considering the characteristic of the filter circuit, can you explain why the distortion occurs? 9. The present position of the DUTY CYCLE SELECTOR switch ('5") indicates that the duration of each sample is 503 of the sampling period (the time between the start of adjacent samples). Variation of the switch setting allows this proportion (called the ·sampling duty cycle le") to be changed from 0% to 90% in 10% steps Using a 32kHz sampling frequency, vary the position of the DUTY CYCLE SELECTOR switch, observing how the SN1PLE OUTPUT changes and how the amplitude of the filters output waveform changes. This amplitude increases linearly as the sampling duty cycle increases from 10% to 90%. 10. Add a link from the SN1PLE OUTPUT to the input of the SECOND ORDER LOW PASS FILTER. Display the outputs of the SECOND ORDER and FOURTH ORDER low pass filters (t.p.44 and t.p.49) on the oscilloscope CF ig.3). With a sampling duty cycle of 503 (DUTY CYCLE SELECTOR switch position '5"), step through the 8kHz, l6kHz and 32kHz sampling frequencies, comparing the filter outputs after each step. Note that, for each sampling frequency, the fourth order output exhibits less distortion than the second order output. This is because the fourth order filter has a sharper ·roll-off' than the second order filter, and thus rejects more frequency components caused by the sampling signal. 11. Remove the links between the SN1PLE OUTPUT and the inputs to the two filters. With a sampling frequency of 32kHz and a sampling duty cycle of 50%, compare the SN1PLE OUTPUT (t.p.33) and the SAMPLE/HOLD OUTPUT (t.p.35) on the oscilloscope (Fig.4). Vary the sampling frequency to illustrate how each sample is held at the sample/hold output. Note how increasing the sampling duty cycle. Increases the proportion of time for which sampling reduces the time for which these samples are held at the SAMPLE/HOLD OUTPUT. 38 12. Link from SAMPLE/HOLD OUTPUT to the input of FOURTH ORDER LOW PASS FILTER. Using a sampling frequency of 32kHz and a duty cycle of 503, display the SAMPLE/HOLD OUTPUT (t.p.35) and the output of the FOURTH ORDER LOW PASS FILTER (t.p.49) on the oscilloscope, to show once again that the original 1kHz sine wave can be reconstructed by low pass filtering (Fig.5). 13. By making successive presses or the FREQUENCY SELECTOR switch, note how the filters output waveform changes with sampling frequency. 14. Using a 32kH Sampling frequency, vary the sampling duty cycle and note that in contrast with the results or step 9 above, The filters outpoll amplitude is now independent of the sampling duty cycle, and 1s is equal to the amplitude of the original analog Input. This is an important result - with the Sample/HOLD OUTPUT, the proportion of sampling t 1me to holding time has no effect on filter output amplitude, providing the sampling frequency Is high enough to recover the original analog waveform In a practical dlg1tal communications system, transmitted samples tend to be of short duration so that as many samples can be transmitted as Possible; at the receiver, each received sample 1s held in a sample/hold circuit before low -pass filtering in order that the filter's output has maximum amplitude 15. Add a link from the SAMPLE/HOLD OUTPUT to the input or the SECOND OOOER LOW PASS FILTER Display the outputs or the Second ORDER LOW PASS FILTER (t.p.44) and FOURTH ORDER LOW PASS FILTER (t.p. 49) on the oscilloscope, and or a sampling duty cycle of 50% Compare the outputs of the two filter for the 8 kHz, 16kHz and 32kHz sampling frequencies. Are these waveforms more or less distorted than those obtained from the SAMPLE OUTPUT in Step 10, for each sampling frequency? 39 YOUR GOAL IS TO OBTAIN THE FOLLOWING 5 WAVEFORMS WITH THE ABOVE-MENTIONED PROCEDURE. 40 41 42 Brac University Department of Electrical and Electronic Engineering EEE/ECE341L/342: Introduction to Communication Engineering Laboratory Experiment No: 3 (Software) Experiment Name:- Frequency Modulation & Demodulation using MATLAB Simulink 1. Objective: To perform the Frequency Modulation signal Generation and Detection using Matlab Simulink. 2. Theoretical Background: Frequency Modulation- To generate a frequency modulated signal, the frequency of the radio carrier is changed in line with the amplitude of the incoming audio signal. When the audio signal is modulated onto the radio frequency carrier, the new radio frequency signal moves up and down in frequency. The amount by which the signal moves up and down is important. It is known as the deviation and is normally quoted as the number of kilohertz deviation. As an example the signal may have a deviation of plus and minus 3 kHz, i.e. ±3 kHz. In this case the carrier is made to move up and down by 3 kHz. Broadcast stations in the VHF portion of the frequency spectrum between 88.5 and 108 MHz use large values of deviation, typically ±75 kHz. This is known as wide-band FM (WBFM). These signals are capable of supporting high quality transmissions, but occupy a large amount of bandwidth. Usually 200 kHz is allowed for each wide-band FM transmission. For communications purposes less bandwidth is used. Narrow band FM (NBFM) often uses deviation figures of around ±3 kHz. It is narrow band FM that is typically used for two-way radio communication applications. Having a narrower band it is not able to provide the high quality of the wideband transmissions, but this is not needed for applications such as mobile radio communication. Frequency demodulation- As with any form of modulation, it is necessary to be able to successfully demodulate it and recover the original signal. The FM demodulator may be called a variety of names including FM demodulator, FM detector or an FM discriminator. There are a number of different types of FM demodulator, but all of them enable the 43 frequency variations of the incoming signal to be converted into amplitude variations on the output. These are typically fed into an audio amplifier, or possibly a digital interface if data is being passed over the system. 3. Software and Device requirement: MATLAB (with Simulink) Minimum PC specifications: Windows/ Mac: Microsoft® Windows® 7 Professional, Enterprise, Ultimate or Home Premium (64-bit); Windows 8 (64-bit) (All Service Packs); Windows 10 (64-bit); Windows 2008 R2 Server; Windows 2012 Server (All Service Packs). Ram: 2 GB Processor: Intel® Pentium® 4 or AMD Athlon XP 2000 with multi-core CPU Display resolutions: 1,024 x 768 display resolution with true color (16-bit color) 4. Problem Statement: ⮚ Draw all the models one-by-one in the MATLAB Simulink window. ⮚ Set the simulation time from the model window as below: Simulation🡪 Simulation parameters: Start time = 0.0 & Stop time = 50.0. ⮚ Then simulate all the models and observe all the wave shapes at different points of the model. Parameters to be used for different blocks- 44 Simulation Model- 5. Lab Report: i. Design FM Modulation and Demodulation circuits using Built-in blocks of MATLAB ii. Write down a short paragraph explaining the functionalities of VCO and how Phase Locked Loop (PLL) method of demodulation works. 45 Brac University Department of Electrical and Electronic Engineering EEE/ECE341L/342: Introduction to Communication Engineering Laboratory Experiment No: 4 (Software) Experiment Name:- Sampling Theorem using MATLAB Simulink 1. Objective: The objective of this experiment is to study the Sampling Theorem. 2. Theoretical Background: Given a continuous sinusoidal signal s(t) and an impulse train p(t) , we can sample continuous signal s(t) by multiplying with p(t). Suppose the period of impulses in p(t) is Ts and its corresponding sampling frequency will be 1 /Ts= Fs. In addition, the continuous sinusoidal signal has frequency F. In this section, we will discuss three cases, Fs < 2F (Sampling rate is less than twice sine wave frequency) Fs = 2F (Sampling rate is equal to twice sine wave frequency) Fs > 2F (Sampling rate is larger than twice sine wave frequency) Fig. 1: Sampling Theorem From sampling theorem, sampling rate Fs should be equal or larger than twice frequency of sinusoidal signal F. i.e., Fs ≥2F. For our Simulink configuration, we set the sinusoidal signal frequency as 500Hz and we give three sampling frequencies, 500Hz, 1kHz and 10kHz. For Nyquist theorem, if the sampling rate is smaller, it will result in aliasing. If the sampling rate is larger than the Nyquist rate, it will result in imaging. Hence, in this section, we want to give a true simulation of sampling a continuous sinusoidal signal and give discussion in “Time Domain”. 3. Software and Device requirement: 46 MATLAB (with simulink) Minimum PC specifications: Windows/ Mac: Microsoft® Windows® 7 Professional, Enterprise, Ultimate or Home Premium (64-bit); Windows 8 (64-bit) (All Service Packs); Windows 10 (64-bit); Windows 2008 R2 Server; Windows 2012 Server (All Service Packs). Ram: 2 GB Processor: Intel® Pentium® 4 or AMD Athlon XP 2000 with multi-core CPU Display resolutions: 1,024 x 768 display resolution with true color (16-bit color) 4. Problem Statement: 1. Draw all the models one-by-one in the MATLAB Simulink window. 2. Set the simulation time from the model window as below: Simulation →Simulation parameters: Start time = 0.0 & Stop time = 0.01. 3. Simulate the model and observe all the wave shapes at different points of the model. 5. Procedure: 1. You can take the blocks from the Simulink Library Browser. a. The blocks that you will use in this experiment can be taken from the following mentioned library: I. Sine Wave: Simulink →Sources→Sine wave II. Pulse Generator: Simulink→ Sources→Pulse Generator III. Product: Simulink→Math operations→Product IV. Scope: Simulink→Sinks→Scope Parameters to be used for different blocks: 1. Sine wave: Sine type:Time based Amplitude: 5.0 Frequency: 2*pi*500 rad/sec Sample time: 1/1000000 2. Pulse Generator: Pulse type: Time based Amplitude: 1.0 Period (secs): 0.0001 Pulse width (% of period): 0.1 3. Product: Number of inputs: 2 & Multiplication: Element wise 4. Scope: Data History: Uncheck the ‘Limit data points to last’. 47 Simulation Models Output- 6. Report: 1. At first regenerate the model shown in the experiment. Then build the model for reconstruction on top of that. Show all the wave shapes in the report of the full model. 2. Explore natural sampling and show the wave shapes in the report. Brac University Department of Electrical and Electronic Engineering 48 EEE/ECE341L/342: Introduction to Communication Engineering Laboratory Experiment No: 5 (Hardware) Experiment Name: - Amplitude Shift-Keying In many situations, for exam ple in radio frequency transmission, data cannot be transmitted directly, but must be used to modulate a higher frequency sinewave carrier. The simplest way of modulating a carrier with a data stream is to change the amplitude of the carrier every time the data changes. This technique is known as amplitude shift-keying. The simplest forn1of amplitude shift-keying is 'on-off keying·, where the transmitter outputs the sinewave carrier whenever the data bit is a ‘1’, and totally suppresses the carrier when the data bit is a ‘0’. In other words, the carrier is turned ‘on’ for a ‘1’, and ‘off’ for a ‘0’. This form of amplitude shift-keying is illustrated in Figure 1 below: In order to generate an amplitude shift-keyed (ASK) waveform at the Transmitter, a balanced modulator circuit is used (also known as a linear multiplier) This device simply multiplies together the signals at its two inputs, the output voltage at any instant in time being the product of the two input voltages. One of the inputs is a.c. coupled; this is known as the carrier input. The other is d.c. coupled, and is k n own as the modulation (or signal ) input. In order to generate the ASK waveform, al1 tr1at is necessary is to connect the sinewave carrier to the carrier input, and the digtal data stream to the modulation input, as shown in Figure 2 overleaf: - 49 The data stream applied to the modulator's modulation input is unipolar, i e. its ‘0’ and ‘1’ levels are 0 volts and +5 volt s respec tively. Consequently: (1) V hen the current data bit is a ·1·, the carrier is multiplied by a constant, positive voltage, causing the carrier to appear, u nchanged in phase, at the modulator's output. (2) When the current data bit is a 'O', the carrier is multiplied by O volt s, giving O volts at the modulator's output. At the Receiver, the circuitry required to demodulate the amplitude Shift-keyed ·waveform is minimal. The simplest method is to rectify the Incoming ASK signal, and then filter it, as shown in Figures 3 (a) and (b) below, respectively. 50 The filter's output appears as a very rounded version of the original data stream, and is still unsuitable f or use by the Receiver's digital circuits. To overcome this, the filter's output waveform is 'squared up' by a voltage comparator, as shown in Figure 14(c). Figure 4 belov-1shovv s the functional blocks required in order to demodulate the ASK waveform at the Receiver: In Experiment 2, we will investigate the generation of the ASK signal at the Transmitter, and its demodulation at the Receiver. EXPERIMENTATION 1. This experiment uses the following four MODICOM boards: 3/1, 3/2, 5/1 and 5/2. We shall use the MODICOM 3/1 and 5/1boards as the transmitter of our communications system, and the MODICOM 5/2 and 3/2 boards as the Receiver. 2. If necessary, check that MODICOM 3/2’s CLOCK REGENERATION CIRCUIT is set up for correct operation. See Chapter 7 (Technical Information) for details on when this needs to be done, and how to do it. 3. Check that the following initial conditions exist on the MODICOM 3/1 board: FAST mode selected; SYNC CODE GENERATOR off; ERROR CHECK CODE SELECTOR switches in A=0, B=0, positions; All switched faults off. 4. Check that the slider of the MODE switch on the MODICOM 5/1 board is in position ‘1’. 5. Ensure that the following initial conditions exist on the MODICOM 3/2 board: FAST mode selected SYNC CODE DETECTOR on ERROR CHECK CODE SELECTOR switches in A=0, B=0 positions; ALL switched faults off; PULSE GENERATOR DELAY ADJUST preset in fully clockwise position. 51 6. Connect up the supplies to the boards, as shown in Figure 16 at the end of this chapter. 7. Turn on power to the boards. 8. Make the following four signal connections: (1) on MODICOM 3/1: D.C 1 to CH.0 input CH.0 input to CH.1 input (2) Between MODICOM’s 3/1 and 5/1: MODICOM 3/1 MODICOM 5/1 TX. CLOCK OUTPUT to TX. CLOCK INPUT TX. DATA OUTPUT to TX. DATA INPUT 9. Connect the oscilloscope’s external trigger input to MODICOM 3/1’s TX. TO OUTPUT signal (t.p.4), and set up the ‘scope for external, negative edge triggering. 10. On the MODICOM 3/1 board, adjust the D.C. 1 preset until the 7-bit code displayed on the board’s A/D CONVERTER L.E.D.’s is: D6 D0 1 0 1 0 0 1 1 11. Examine the DATA CLOCK output in MODICOM 5/1’s DATA CONDITIONING CIRCUITS block (t.p.4). It may be necessary to adjust the ‘scope’s trigger level manually, in order to obtain a stable trace. Adjust the ‘scope’s time base and X-position controls until each rising edge of the data clock coincides with one of the ‘scope’s vertical graticule lines, as shown in Figure 17 below. Once this has been done, each main division on the ‘scope’s horizontal axis will represent one data bit time. 52 12. Connect up the MODICOM 5/1, 5/2 and 3/2 boards as shown in Figure 18 at the end of the chapter, and monitor the NRZ(L) output (t.p.5) from MODICOM 5/1’s DATA CONDITIONING CIRCUITS block. On the other ‘scope channel. Monitor the output of MODULATOR 1 ((t.p.30) in MODICOM 5/1’s CARRIER MODULATION CIRCUITS block. 13. To obtain the ASK waveform shown in Figure 12 (at the start of the chapter), it may be necessary to adjust MODULATOR 1’s MODULATION OFFSET, CARRIER OFFSET and GAIN presets. Each of these presets has the following effect on the monitored wave form: MODULATION OFFSET: this adjusts the amplitude of the ‘off’ signal adjust this until the amplitude of the ‘off’ signal is as close to zero as possible. CARRIER OFFSET: this adjusts the ‘off’ bias level of the amplitude-modulated sine wave. Adjust this preset until the ‘off’ level occurs midway between the peaks of the ‘on’ signal. GAIN: this adjusts the amplitude of the modulator’s output. Adjust this preset until the amplitude of the ‘on’ signal is 2 volts pk/pk. 14. To understand how the ASK waveform is demodulated at the Receiver, examine the output of the ASK DEMODULATOR (t.p.22) and the output of FILTER 1(t.p.24) on the MODICOM 5/2 board. 15. The final stage of the demodulation process is to ‘square up’ the filter’s output signal. In order to achieve this, it is first necessary to adjust COMPARATOR 1’s BIAS level so that the output pulses from COMPARATOR 1 have the correct pulse width. Adjust COMPARATOR 1’s BIAS preset until the pulses at the comparator’s output (t.p.33) have the same duration as those at MODICOM 5/1’s NRZ(L) output (t.p.5). Once this has been done, the two waveforms should appear identical, except for a short time delay between them. 53 16. Turn on MODICOM 3/1’s SYNC CODE GENERATOR. 17. The system should now be a fully operational ASK Transmitter-Receiver system. Change the position of MODINOM 3/1’s D.C. 1 preset. And check that the 7-bit codes in MODICOM 3/1‘s A/D CONVERTER block and MODICOM 3/2’s D/A CONVERTER block are always the same, indicating that frame synchronization has been achieved. 18. If desired, try connecting MODICOM 3/1’s ~1kHz and ~2kHz FUNCTION GENERATOR outputs to the board’s CH.0 and CH. 1 analog inputs, and check that these are reconstructed at MODICOM 3/2’s analog outputs. 19. In this experiment, the carrier signal has been amplitude-modulated by MODICOM 5/1’s NRZ(L) output. Equally, any of the other outputs from the board’s DATA CONDITIONING CIRCUITS block could have been used to modulate the carrier. If you wish, you can experiment with these other data representations. Demodulating the carrier ad described above. And converting the data back to NRZ(L) format by means of the data reconditioning techniques described in Experiment 1. 20. Although MODICOM 5/1’s 1.44MHz sine wave output was used as the carrier signal in this experiment, the 960kHz(1) output could equally have been used, with no further adjustment of the system being necessary 54 55 56 Brac University Department of Electrical and Electronic Engineering EEE/ECE341L/342: Introduction to Communication Engineering Laboratory Experiment No: 6 (Hardware) Experiment Name: - Frequency Shift-Keying In Frequency Shift-Keying, the signal at the Transmitter's output is switched from one frequency to another, every time there is a change in the level of the modulating data stream For example, if the higher frequency is used to represent a data ' 1', and the lower frequency a data '0', the resulting Frequency Shift-Keyed (FSK) waveform might appear as shown in Figure 1 below: Figure: 1 The generation of an FSK waveform at the Transmitter can be achieved by generating two ASK waveforms and adding them together with a summing amplifier. This is illustrated m Figure 2 below: 57 Figure: 2 The functional blocks required in order to generate the FSK signal are shown in Figure 3 below. Note that the sine wave frequency at the carrier input of each modulator is different, and that the data at the modu l ation input of one i s the inverse of that at the modulation input of the other. Figure: 3 58 At the Receiver, the frequency shift-keyed signal is decoded by means of a phase- locked loop (PLL) detector. The detector follows changes i n frequency in the FSK signal, and generates an output voltage proportional to the signal frequency. The phase-locked loop’s output also contains components at the two carrier frequencies; a low-pass filter is used to filter these components out. The filter's output appears as a very rounded version of the original data stream, and i s still unsuitable f or use by the Receiver’s digital circuits. To overcome this, the filter’s output waveform i s ·squared up· by a voltage comparator. Figure 4 overleaf shows the functional blocks required in order to demodulate the FSK waveform at the Receiver: Figure: 4 In Experiment 3, we will investigate the generation of the FSK signal at the Transmitter, and its demodulation at the Receiver. EXPERIMENTATION 1. This experiment uses the following four MODICOM boards: : 3/1, 3/2, 5/1 and 5/2. We shall use the MODICOM 3/1 and 5/1boards as the transmitter of our communications system, and the MODICOM 5/2 and 3/2 boards as the Receiver. 2. If necessary, check that MODICOM 3/2’s CLOCK REGENERATION CIRCUIT is set up for correct operation. See Chapter 7 (Technical Information) for details on when this needs to be done, and how to do it. 3. Check that the following initial conditions exist on the MODICOM 3/1 board: FAST mode selected; SYNC CODE GENERATOR off; ERROR CHECK CODE SELECTOR switches in A=0, B=0, positions; All switched faults off. 4. Check that the slider of the MODE switch on the MODICOM 5/1 board is in position ‘1’. 59 5. Ensure that the following initial conditions exist on the MODICOM 3/2 board: FAST mode selected SYNC CODE DETECTOR on ERROR CHECK CODE SELECTOR switches in A=0, B=0 positions; ALL switched faults off; PULSE GENERATOR DELAY ADJUST preset in fully clockwise position. 6. Connect up the supplies to the boards, as shown in Figure 16 at the end of this chapter. 7. Turn on power to the boards. 8. Make the following four signal connections: (1) on MODICOM 3/1: D.C 1 to CH.0 input CH.0 input to CH.1 input (2) Between MODICOM’s 3/1 and 5/1; MODICOM 3/1 MODICOM 5/1 TX. CLOCK OUTPUT to TX. CLOCK INPUT TX. DATA OUTPUT to TX. DATA INPUT 9. Connect the oscilloscope’s external trigger input to MODICOM 3/1’s TX. TO OUTPUT signal (t.p.4), and set up the ‘scope for external, negative edge triggering. 10. On the MODICOM 3/1 board, adjust the D.C. 1 preset until the 7-bit code displayed on the board’s A/D CONVERTER L.E.D.’s is: D6 D0 1 0 1 0 0 1 1 11. Examine the DATA CLOCK output in MODICOM 5/1’s DATA CONDITIONING CIRCUITS block (t.p.4). It may be necessary to adjust the ‘scope’s trigger level manually, in order to obtain a stable trace. Adjust the ‘scope’s time base and X-position controls until each rising edge of the data clock coincides with one of the ‘scope’s vertical gratitude lines, as shown in Figure 5 over leaf. 60 Figure 5 Once this has been done, each main division on the ‘scope’s horizontal axis will represent one data bit time. 12. Make the connections shown in Figure 25 at the end of this chapter. 13. On the oscilloscope, monitor the output of MODULATOR 1 (t.p.30) in MODICOM 5/1’s CARRIER MOFULATION CIRCUITS block. Adjust MODULATOR 1’s MODULATION OFFSET, CARRIER ORRSET and GAIN presets, in order to obtain the ASK signal shown in Figure 6 below Each of these presets has the following effect on the monitored waveform. MODULATION OFFSET: this adjusts the amplitude of the ‘off’ signal. Adjust this until the amplitude of the ‘off’ signal is as close to zero as possible. CARRIER OFFSET: this adjusts the ‘off’ bias level of the amplitude-modulated sine wave. Adjust this preset until the ‘off’ level occurs midway between the peaks of the ‘on’ signal. GAIN: this adjust the amplitude of the modulator’s output. Adjust this preset until the amplitude of the ‘on’ signal is 2 volts pk/pk. 61 Figure 6 14. Repeat the previous step with MODICOM 5/1’s MODULATOR 2. This time, monitor MODULATOR 2’s output at t.p.33, and adjust the modulator’s MODULATION OFFSET, CARRIER OFFSET and GAIN controls as described above, until the modulator’s output is as shown in Figure 7 below: Figure 7 15. Examine the output of MODICOM 5/1’s SUMMING AMPLIFIER block (t.p.36), and note that this carries a frequency shift-keyed (FSK) signal. If necessary, adjust the GAIN control of the MODULATOR 2 so that the two frequency components of the DSK signal are of equal amplitude. 16. While monitoring the FSK signal, display MODICOM 5/1’s NRZ(L) output (t.p.5) on the other ‘scope channel. Note that the FSK signal is at its lower frequency (960kHz) when the data bit is a ‘0’, and change to its higher frequency (1.44MHz) whenever the data bit becomes a ‘1’. 17. To see how the FSK waveform is demodulated at the Receiver, examine the input (t.p.16) and the output (t.p.17) of MODICOM 5/2’s FSK DEMODULATOR block (t.p.17). Note that the output voltage of the demodulator is greater for the higher incoming frequency than it is for the lower incoming frequency. Notice also that, for both incoming carrier frequencies, the demodulator’s output also contains a component at that frequency. 18. The next stage is to remove these unwanted carrier frequency components by low pass filtering. Examine the input (t.p.23) and output (t.p.24) of MODICOM 5/2’s FILTER 1 (in the LOW PASS FILTERS block), and check, that the unwanted frequency components are removed by the low pass filter. 19. The final stage of the demodulation process is to ‘square up’ the filter’s output signal. In order to achieve this, it is first necessary to adjust COMPARATOR 1’s BIAS level (in MODICOM 5/2’s DATA SQUARING 62 CIRCUITS block) so that the output pulses from COMPARATOR 1 have the correct pulse width. Adjust COMPARATOR 1’s BIA5 preset until the pulses at the comparator’s output (t.p.33) have the same duration as those at MODICOM 5/1’s NRZ(L) output (t.p.5). Once this has been done, the two waveforms should appear to be identical, except for a time delay between them. 20. Turn on MODICOM 3/1’s SYNC CODE GENERATOR. 21. The system is now a fully operational FSK Transmitter-Receiver system. Change the position of MODICIM 3/1’s D.C. 1 preset, and check that the 7-bit codes in MODICOM 3/1’s A/D CONVERTER block and MODICOM 3/2’s D/A CONVERTER block are always the same. 22. If desired, try connecting MODICOM 3/1’s ~1kHz and ~2kHz FUNCTION GENERATOR outputs to the board’s CH.0 and CH.1 analog inputs, and check that these are reconstructed at MODICOM 3/2’s analog outputs. 23. In this experiment, the carrier signal has been frequency-modulated by MODICOM 5/1’s NRZ(L) output. Equally, any of the other binary outputs from the board’s DATA CONDITIONING CIRCUITS block could have been used to modulate the carrier. If you wish, you can experiment with these other data representations, demodulating the carrier as described above, and converting the data back to NRZ(L) format by means of the data reconditioning techniques described in Experiment 1. 63 64 65 Brac University Department of Electrical and Electronic Engineering EEE/ECE341L/342: Introduction to Communication Engineering Laboratory Experiment No: 5 (Software) Experiment Name:- Digital Pass band Modulation and Demodulation using MATLAB Simulink 1. Objective: The objective of this experiment is to study the digital modulation techniques such as OOK, ASK, FSK and PSK pass band modulation and demodulation using MATLAB Simulink. The transmitted binary sequence, the modulated and the demodulated signals will be observed in this experiment. An AWGN channel will be taken as the transmission medium. 2. Theoretical Background: In a digital baseband system, the signals are transmitted directly over a pair of wires, coaxial cables, or optical fibers without any shift in frequencies of the signal. To remove the limitations of the antenna size required to transmit baseband digital signal, and for efficient use of the available frequency spectrum, passband transmission is suitable for transmission over radio links or satellites. Passband transmission is achieved by modulating a high frequency carrier signal by the baseband digital signal. In amplitude shift keying (ASK) and on-off keying (OOK), the amplitude of the carrier signal is varied with the amplitude of the digital signal. In frequency shift keying (FSK), the frequency and in phase shift keying (PSK), the phase of the carrier signal is varied with the amplitude of the digital baseband modulating signal respectively. 3. Software and Device requirement: MATLAB (with Simulink) Minimum PC specifications: Windows/ Mac: Microsoft® Windows® 7 Professional, Enterprise, Ultimate or Home Premium (64-bit); Windows 8 (64-bit) (All Service Packs); Windows 10 (64-bit); Windows 2008 R2 Server; Windows 2012 Server (All Service Packs). Ram: 2 GB Processor: Intel® Pentium® 4 or AMD Athlon XP 2000 with multi-core CPU Display resolutions: 1,024 x 768 display resolution with true color (16-bit color) 4. Problem Statement: (i) Draw all the models one-by-one in the MATLAB Simulink window. (ii) Set the simulation time from the model window as below: Simulation🡪Simulation parameters: Start time = 0.0 & Stop time = 10.0. (iii) Then simulate all the models and observe all the wave shapes at different points of the model. 5. Procedure: ⮚ You can take the blocks from the Simulink Library Browser. ⮚ The blocks that you will use in this experiment can be taken from the following mentioned library: (i) Bernoulli Binary Generator: Communication Blockset🡪 Comm sources🡪Data🡪Sources🡪Bernoulli Binary Generator 66 (ii) Sine Wave: Simulink🡪 Sources🡪Sine wave (iii) Product: Simulink🡪Math operations🡪Product (iv) AWGN Channel: Communication Block Set🡪Channels🡪AWGN Channel (v) Digital Filter Design: Communication Blockset🡪Comm Filters🡪Filter Designs🡪Library Link🡪Digital Filter Design (vi) Spectrum Scope: Signal Processing Blockset🡪Signal Processing Sinks🡪Spectrum Scope (vii) Compare to Constant: Simulink🡪Logic & Bit Operations🡪Compare to Constant (viii) Scope: Simulink🡪Sinks🡪Scope (ix) Constant: Simulink🡪Sources🡪Constants (x) Abs: Simulink🡪Math operations🡪Abs (xi) Sum: Simulink🡪Math Operations🡪Sum Parameters to be used for different blocks- 67 Simulation Models- 68 6. Lab Report: 1. Submit wave forms and frequency spectrums in printed form those you have observed in your lab. 2. Use an AWGN channel between the modulator and demodulator circuits for OOK and ASK. Describe the effects of noisy channel on Demodulation. 3. Construct demodulation circuits for FSK and PSK. Take help from theory lectures and internet. Brac University Department of Electrical and Electronic Engineering EEE/ECE341L/342: Introduction to Communication Engineering Laboratory Experiment No: 6 (Software) Experiment Name:- Digital Pass Band Modulation and Demodulation using MATLAB Simulink (FSK & PSK) 1. Objective: The objective of this experiment is to study the digital modulation techniques such as FSK and PSK pass band modulation and demodulation. 2. Problem Statement: At first, the binary sequence is transmitted, then the modulated and the demodulated signals will be observed in this experiment. An AWGN channel will be taken as the transmission medium. 69 3. Software and Device requirement: MATLAB Minimum PC specifications: Windows/ Mac: Microsoft® Windows® 7 Professional, Enterprise, Ultimate or Home Premium (64-bit); Windows 8 (64-bit) (All Service Packs); Windows 10 (64-bit); Windows 2008 R2 Server; Windows 2012 Server (All Service Packs). Ram: 2 GB Processor: Intel® Pentium® 4 or AMD Athlon XP 2000 with multi-core CPU Display resolutions: 1,024 x 768 display resolution with true color (16-bit color) 4. Circuit Diagram/ Experimental setup: 70 5. Procedure: You can take the blocks from the Simulink Library Browser. The blocks that you will use in this experiment can be taken from the following mentioned library: Bernoulli Binary Generator: Communication Blockset→Comm sources→Data Sources→Bernoulli Binary Generator. Sine Wave: Simulink→Sources→Sine wave Product: Simulink→Math Operations→Product. AWGN Channel: Communication Block SetChannelsAWGN Channel. Digital Filter Design: Communication Blockset→Comm Filters→Filter Designs Library Link→Digital Filter Design. Spectrum Analyzer : DSP System ToolBox→Sinks→Spectrum Analyzer. Parameters to be used for different blocks: Bernoulli Binary Generator: Probability of Zero = 0.5, Initial seed = 61, Sample time = 1(for ASK & ON-OFF) and 1/10 (for FSK & PSK), Uncheck the ‘Frame-based outputs’ & ‘Interpret Vector Parameters as one dimensional’. Spectrum Analyzer : Spectrum Settings→Type : RMS , Trace Option →select “two-sided spectrum”. Sine wave: For FSK: Sine type: Time based Amplitude: 1.0 Frequency: 2*pi*2000 (carrier for ‘1’ & sine wave 1) & 2*pi*1000 (carrier for ‘0’ & sine wave 0). Sample time: 1/5000 For PSK: Sine type: Time based Amplitude: 1.0 Frequency: 2*pi*1000 rad/sec Sample time: 1/5000 Product: Number of inputs: 2 & Multiplication: Element wise. AWGN Channel: Initial seed: 67, Mode: Variance from mask & variance: 1. (Note: You can vary the noise power by varying variance) Digital Filter Design: Filter type: Low Pass. Design method: FIR→Equiripple. Filter order: Minimum order. Frequency Specifications: Units: Hz, FS: 5000, FPass=15, FStop=55. (FSK) Magnitude Specifications: Units: dB, Apass=1, Astop=80. Then click Design Filter. The magnitude response of the filter will be changed according to your specifications. Note: You should choose your Fpass and Fstop frequencies depending on the frequency of your modulating signal 71 Compare to constant: Operator: >=. Constant: Depends on your system. This is the threshold value of the detector. Scope: Data History: Uncheck the ‘Limit data points to last’. Constant: Constant value: 1 Abs: Check the ‘saturate on integer overflow’ & ‘Enable zero crossing detection’ Sum: List of signs: |+- (subtraction will be done). (Note: To sum up two inputs, list of signs: |++) 6. Lab report directions/ Questions/ Discussions/ Assignments: A. Submit waveforms and frequency spectrums in printed form to those you have observed in your lab. B. Change FPass and FStop for all the filters to 100 Hz and 200 Hz respectively for both models. Then observe both the input and the output wave shapes and frequency spectrums for both models. Is there any discrepancy between the input and the output wave shapes? If so, explain why? C. Increase the variance in the AWGN channel block to 10 and 100. Is there any effect of this change on the output wave shapes and frequency spectrums? If any, what are the changes? D. “The received signal in analogue communication is distorted more by the channel noise than that of digital communication” – If you agree with this statement, then explain why? PROJECT Design and simulation of a communication link using AM Expected Outcomes: To have built communication links using existing AM modulation and demodulation blocks, constructed AM modulators using operational function blocks based on their mathematical expressions, and conducted simulations of the links and modulators, all in Simulink. Detailed Requirements: Use Simulink to design a communication link for AM audio broadcasting. The message signal is a mono audio signal although you may not be able to transmit the full audio frequency range that is normally required for high quality sound. 72 The specification for the link is as follows: Required signal to noise ratio (SNR) at the demodulated audio output of the receiver: 40 dB for a 1 kHz message signal at 50% modulation (m = 0.5). ▪ Carrier frequency: 1.35 MHz ▪ Maximum RF bandwidth available 9 kHz ▪ Channel noise power spectral density = -150dBm/Hz Find out the followings for Task-01: 1. What is the highest frequency of the message signal that can be transmitted without exceeding the specified RF bandwidth? 2. For this message frequency, save a time domain plot and a frequency domain plot showing the modulated RF output from the transmitter. 3. How much carrier power is required in order to achieve the required SNR? For this carrier power, how much power is there in each sideband for the m = 0.5? 4. What is the SNR at the demodulated output if the frequency of the message signal is changed to the following frequencies? 200 Hz The highest frequency that can be transmitted without exceeding the specified RF bandwidth. What is the SNR at the demodulated output if the modulation index m is increased to 1? 5. What happens if m > 1, if m = 1.5? Compare the demodulated output from the receiver in the time domain and in the frequency domain for m = 1 and m = 1.5 and explain why a modulation index greater than 1 must be avoided in an AM link. Prompts: In order to complete the work required in the above, you will need to Generate baseband and carrier sinewave signals and AWGN noise Construct a channel model with constant loss and AWGN noise Construct an AM modulator with operational function blocks based on time-domain AM expression Construct a communications link using the built AM modulator, built channel model, and exiting AM demodulator block in Simulink. 73 Design and simulation of communication links using PSK Expected Outcomes: To have built communication links using existing PSK modulation and demodulation blocks, constructed PSK modulators using operational function blocks based on their mathematical expressions, and conducted simulations of both links and modulators, all in Simulink. Key Tasks: Generate baseband binary signals and carrier sinewave signals and AWGN noise Simulate and evaluate a communications link using BPSK with existing mod and de-mod blocks Simulate and evaluate a communications link using QPSK with existing mod and de-mod blocks Construct a BPSK modulator with operational function blocks based on the ti

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