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Laboratory 10: Communication

Laboratory 10: Communication. General Engineering Polytechnic University. Objective Transmission of Media LASER Fiber-Optics Signal Forms Number Systems and Codes. Conversions Error Detection Error Correction Materials for Lab Procedure Written Assignment Recitation Topics Closing.

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Laboratory 10: Communication

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  1. Laboratory 10:Communication General Engineering Polytechnic University

  2. Objective Transmission of Media LASER Fiber-Optics Signal Forms Number Systems and Codes Conversions Error Detection Error Correction Materials for Lab Procedure Written Assignment Recitation Topics Closing Overview

  3. Objectives • Learn the principles of free-space laser communication systems • Study the fundamentals of analog fiber-optic communications • Measure the frequency response of a fiber-optic link, and find its bandwidth • Demonstrate how digital data from a computer can be transmitted optically • Learn about computer ASCII characters • Learn the difference between analog and digital message signals

  4. Transmission of Media • There are two types: • Guided - Signal travel through a cable Uses: Telephone • Non-Guided - Signal travels through air Uses: AM & FM Radio, Television

  5. LASER (Non-Guided) • Powerful: Contains one frequency of light and the waves are coherent (in phase) • A light bulb has many frequencies of light and the waves incoherent (out of phase), making it weak L A S E R ight mplification by timulated mission of adiation

  6. Applications Industry diamond cutting shape machine tools Scientific Research study molecular structures of matter Communication television telephone computers Medicine surgery eyes Military missile guidance LASER (Non-Guided)

  7. Light in Light out Fiber-Optics (Guided) • Made of glass • The light that travels through the cable is a LED (light emitting diode) • Uses the principle of Total Internal Reflection • Light goes through cable by bouncing off the glass walls • The light & signal gets reflected back into the medium

  8. Advantages Transmits date faster than conventional means More than one signal can be sent at the same time No line of sight Disadvantages Expensive Transmission is lost if cable is cut or bent Fiber-Optics (Guided)

  9. Signal Forms • Analog - The signal is continuous (infinite number of states), ranging between a high and low voltage Voltage (V) Time (sec)

  10. Signal Forms • Digital - The signal is discreet (only 2 states), there is no range only “on’s” and “off’s” • Active High (high=1) • Active Low (low=1) • Digitizing - Converting an analog signal to a digital signal Voltage (V) 0 0 0 0 Active Low  1 1 1 Time (sec)

  11. Number Systems and Code • American Standard Code for Information Interchange (ASCII) • Each alphanumeric character is coded so that it can be stored and read by the computer • Each character is given a specific number or code • An abbreviated chart can be found on page 92 • Number Systems • Decimal • Based on 10 possible values; 0 to 9 57610 = (5*102) + (7*101) + (6* 100) = 500 + 70 + 6 = 576 • Binary • Based on 2 possible values; 0 and 1

  12. 2 Read Down 2 2 ) ) ) ) 2 1310 Conversions • Binary to Decimal • Similar to expanding a decimal number 11012 = (1*23) + (1*22) + (0*21) + (1*20) = 8 + 4 + 0 + 1 = 1310 • Decimal to Binary • Continue to divide the decimal number by 2, until the quotient reaches zero • The remainder values become the binary value 0 R1 1 R1 3 R0 1310 = 11012 6 R1

  13. NOTE: 8 bits = 1 byte Error Detection • Whenever a signal is sent, there is possibility for error • Error can be detected by • Redundancy - repeating the entire message and comparing the two transmissions (wastes channel and storage capacity) • Parity Bit - A bit added on to a 7-bit character so the byte has an even or odd number of 1’s (only can be used to detect a single-bit error)

  14. Error Correction • Error can be corrected by • Vertical & Horizontal Parity Check • Arrange message in 4 x 4 array • Choose parity bits to make all columns and rows have even (or odd) number of 1’s • Hamming Code • Place message bits in overlapping circles • Choose parity bits, so each circle has even parity

  15. Message Received 1110 1010 0011 0101 Message Sent 1110 1010 0111 0101 Message Sent 1110 1010 0111 0101 1 1  Horizontal Parity Bit 1 1 1 1 1 1 0 0 1 1 0 0 1 1 0 0 0 0 0 1 1 1 1 1 0 0 1 1 0 0 1 1  Vertical Parity Bit Vertical & Horizontal Parity Check Message Sent 1110 1010 0111 0101 Message Place a 1 to get even amount of one’s 1  still even NOTE: The parity bits do NOT change 0  still even  Place a 0 to keep even amount of one’s WRONG BIT Place a 1 to get even amount of one’s 1 ODD! 0  still even  Place a 0 to keep even amount of one’s 0 1 1 0  Place a 1 to get even amount of one’s  still even  still even  Place a 0 to keep even amount of one’s ODD!  Place a 1 to get even amount of one’s  Place a 0 to keep even amount of one’s  still even

  16. P1 P2 Message Received M1 1 M2 0 M3 0 M4 1 Message Sent M1 1 M2 0 M3 1 M4 1 Message Sent M1 1 M2 0 M3 1 M4 1 Message Sent M1 1 M2 0 M3 1 M4 1 Place 1 to get even amount of one’s in pink circle Place 0 to keep even amount of one’s in gray circle P3 P1 M1 P3 P3 P2 Only message bit in all the “ODD” circles therefore… P2 M4 M3 M2 P2 P1 Place 0 to keep even amount of one’s in green circle ODD amount of ones (BAD!) Save circle for later Hamming Code ODD amount of ones (BAD!) Save circle for later Even amount of ones (GOOD!) Disregard circle NOTE: Parity bits do NOT change Message Sent M1 1 M2 0 M3 1 M4 1 0 1 1 1 1 1 WRONG BIT 0 0 1 0 0

  17. Function Generator 1 BNC connector Amplified Speaker 2 Coax cables (BNC to alligator clip) 4 miniature clip leads Computer with LabVIEW Oscilloscope Fiber-optic Trainer Transmitter Receiver 5-meter fiber-optic cable Materials for Lab

  18. Procedure • Laser Demonstration - Performed by Instructors • Components: • Audio Cassette Recorder - Source of the music, modulates the intensity of the laser • Helium-neon Laser - What the music will travel along, optical transmitter • Photo-diode - Responds to the light and produces a electrical signal proportional to the music signal, recovering the music, optical receiver, demodulates laser beam • Speaker - Destination of the music • Laser Demonstration • Fiber-Optic Communication System - Analog • TCP/IP Communication System -Digital

  19. Cassette Recorder Helium-Neon Laser Music Signal Light Free-Space Music Signal Speaker Photo-Diode Procedure • Laser Demonstration - Performed by Instructors • Laser Demonstration • Fiber-Optic Communication System - Analog • TCP/IP Communication System - Digital

  20. Procedure • Laser Demonstration - Performed by Instructors • Laser Demonstration • Fiber-Optic Communication System - Analog • TCP/IP Communication System - Digital

  21. Procedure • Fiber-Optic Communication System - Analog • Turn on the transmitter and receiver circuit boards of the fiber-optic trainer & set the slide switch to “Analog” on both boards • Connect the boards together with the use of the fiber-optic cable • Connect the speaker to the receiver using two miniature clip leads • Speak into the microphone on the transmitter board while your partner listens to the speaker at the receiver’s side • Unplug the fiber-optic cable from the receiver input to observe the visible light beam emitted from the cable • Laser Demonstration • Fiber-Optic Communication System - Analog • TCP/IP Communication System - Digital

  22. Analog Fiber-Optic Receiver (with Audio Power Amplifier) Analog Fiber-Optic Transmitter (with Microphone) 5-Meter Critical Fiber Speaker Procedure • Fiber-Optic Communication System - Analog • Laser Demonstration • Fiber-Optic Communication System - Analog • TCP/IP Communication System - Digital • NOTE: Setup Diagram A on page 90

  23. Procedure • Fiber-Optic Communication System - Analog • Adjust the function generator to produce 200mV peak-to-crest (0.2 V), 1 kHz sine wave • Connect the function generator, the DAQ board and the circuit boards according to Diagram B on page 91 • Measure the gain vs. frequency (f) and complete the data sheet on page 91 • Vout denotes the amplitude of the sinusoidal voltage appearing at the receiver's output • Vin represents the amplitude of the sinusoidal transmitter input signal • Laser Demonstration • Fiber-Optic Communication System - Analog • TCP/IP Communication System - Digital

  24. Function Generator 200mV peak-to-crest Sine Wave Analog Fiber-Optic Receiver (with Audio Power Amplifier) Analog Fiber-Optic Transmitter 5-Meter Critical Fiber Vout Vin LabVIEW Oscilloscope Procedure • Fiber-Optic Communication System - Analog • Laser Demonstration • Fiber-Optic Communication System - Analog • TCP/IP Communication System - Digital • NOTE: Setup Diagram B on page 91

  25. Procedure • TCP/IP Communication System - Digital • Establish a connection between two computers by using the ‘Talk Active’ and ‘Talk Passive’ VIs • Type a message (e.g. “HELLO BETH”) and click the send button on the VI. • Sent messages are displayed in the “Local” window • Received messages are displayed in the “Remote” window • Disconnect the computers and reconnect them using the ‘Writer’ and ‘Reader’ VIs • Type in a message (16 characters or less) on the transmitting computer • Compare the number displayed on the receiving computer with the ASCII code on page 92and find the corresponding alphanumeric character • Laser Demonstration • Fiber-Optic Communication System - Analog • TCP/IP Communication System - Digital

  26. Written Assignment • Full Team Report (one report per team) • Use the guidelines on page 5 for help • Create a graph of gain vs frequency of the table you completed on page 91 • Be sure to use a log scale for the x-axis • Find the 3dB point and bandwidth of your communication system • Make sure your instructor initials your original data • Include the topics found on the next slide • Remember to create a title page

  27. Written Topics • Each of the following topics must be addressed in the full report and should be placed in the proper sections • Explain the lab demonstration on the laser communication system • What is the significance of the bandwidth measurement of the frequency response graph? • From your result would you say your fiber-optic-link is capable of transmitting video signals from a camcorder which requires frequencies of about 5 MHz? • Describe the results obtained with the TCP/IP connection you set up. Were there any problems? • Summarize the advantages of fiber-optic systems. Are there any disadvantages?

  28. Recitation Topics • Discuss the differences between analog and digital signals • Discuss the relative strengths and weaknesses of the three communication media covered in this lab. • Discuss the relationship between bandwidth and frequency as they relate to gain, baud rate, and scan rate

  29. Closing • Return all the equipment back to your instructor

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