laboratory 10: communication general engineering polytechnic university

Laboratory 10:Laboratory 10:CommunicationCommunication

General Engineering

Polytechnic University

OverviewOverview

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

ObjectivesObjectives

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

Transmission of MediaTransmission of Media

There are two types:

– Guided - Signal travel through a cableUses: Telephone

– Non-Guided - Signal travels through airUses: AM & FM Radio,

Television

LASER (Non-Guided)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

LL

AA

SS

EE

RR

ightight

mplification mplification byby

timulatedtimulated

mission ofmission of

adiationadiation

LASER (Non-Guided)LASER (Non-Guided)

Applications– Industry

diamond cutting shape machine

tools

– Scientific Research study molecular

structures of matter

– Communication television telephone computers

– Medicine surgery eyes

– Military missile guidance

Fiber-Optics (Guided)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

Light in Light out

Fiber-Optics (Guided)Fiber-Optics (Guided)

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

Signal FormsSignal Forms

Analog - The signal is continuous (infinite number of states), ranging between a high and low voltage

Time (sec)

Voltage (V)

Signal FormsSignal 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

0

1Active Low

1 1

0 0 0

Time (sec)

Voltage (V)

Number Systems and CodeNumber 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

ConversionsConversions

Binary to Decimal– Similar to expanding a decimal number– 11012 = (1*23) + (1*22) + (0*21) + (1*20)

= 8 + 4 + 0 + 1 = 1310

)2 1310

)2

6 R1)2

3 R0)2

1 R1

0 R1

Read

Do

wn

1310 = 11012

Decimal to Binary– Continue to divide the decimal number by 2, until

the quotient reaches zero– The remainder values become the binary value

Error DetectionError 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)

NOTE: NOTE: 8 bits = 1 byte8 bits = 1 byte

Error CorrectionError 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

Vertical & Horizontal Parity CheckVertical & Horizontal Parity Check

MessageMessage Horizontal Parity Horizontal Parity BitBit

Vertical Parity Vertical Parity BitBit

00

00

11

1100 111111

00 00 1111

00 0011 11

Place a 0 Place a 0 to keep even to keep even amount of amount of one’sone’s

Place a 1 Place a 1 to get even to get even amount of amount of one’sone’s

Place a 1 to Place a 1 to get even amount get even amount of one’sof one’s

Place a 0 to Place a 0 to keep even keep even amount of one’samount of one’s

Place a 1 Place a 1 to get even to get even amount of amount of one’sone’s

Place a 0 Place a 0 to keep even to keep even amount of amount of one’sone’s

Place a 0 to Place a 0 to keep even keep even amount of one’samount of one’s

Place a 1 to Place a 1 to get even amount get even amount of one’sof one’s

11 0011 11

00 001111

11 0011 11

00 001111

00 00 1111

1100 111100

still evenstill even



still evenstill even still evenstill even still evenstill even

ODD!ODD!

ODD!ODD!

WRONGWRONG

BITBIT

Message SentMessage Sent

1110 1010 0111 01011110 1010 0111 0101

NOTE: The NOTE: The parity bits do parity bits do NOT changeNOT change


1110 1010 0111 01011110 1010 0111 0101

Message Sent

1110 1010 0111 0101

Message ReceivedMessage Received

1110 1010 0011 01011110 1010 0011 0101

Hamming CodeHamming Code

P3

P1P2 P1P2

P3


MM1 1 11

MM22 0 0

MM3 3 11

MM4 4 1100 11

11

11

P1

1

P2

P3

P2

M4

M3M2

M1

0 1

0

1

0

Place 0 to keep Place 0 to keep even amount of even amount of one’s in gray one’s in gray circlecircle

Place 1 to get Place 1 to get even amount of even amount of one’s in pink one’s in pink circlecircle

0Place 0 to keep even Place 0 to keep even amount of one’s in amount of one’s in green circlegreen circle

ODD amount of onesODD amount of ones

((BAD!BAD!))

Save circle for laterSave circle for later

ODD amount of onesODD amount of ones

((BAD!BAD!))

Save circle for laterSave circle for later

Even amount of ones Even amount of ones ((GOOD!GOOD!))

Disregard circleDisregard circle

Only message bit in Only message bit in allall the “ODD” circles the “ODD” circles therefore…therefore… WRONG WRONG

BITBIT

NOTE: Parity bits do NOTE: Parity bits do NOT changeNOT change


MM1 1 11

MM22 0 0

MM3 3 11

MM4 4 11


MM1 1 11

MM22 0 0

MM3 3 11

MM4 4 11

Message Sent

M1 1

M2 0

M3 1

M4 1

Message ReceivedMessage Received

MM1 1 11

MM22 0 0

MM3 3 00

MM4 4 11

Materials for LabMaterials for Lab

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

ProcedureProcedure

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 Laser DemonstratioDemonstrationn

•Fiber-Optic Fiber-Optic CommunicatiCommunication System - on System - AnalogAnalog

•TCP/IP TCP/IP CommunicatiCommunication System -on System -DigitalDigital

ProcedureProcedure


Performed by Instructors•Laser Laser DemonstratioDemonstrationn


•TCP/IP TCP/IP CommunicatiCommunication System - on System - DigitalDigital

Cassette

Recorder

Helium-Neon

Laser

Photo-DiodeSpeaker

Music Signal Light Free-Space

Music Signal

ProcedureProcedure


Performed by Instructors•Laser Laser DemonstratioDemonstrationn



ProcedureProcedure 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




ProcedureProcedure

Fiber-Optic Communication System - Analog•Laser Laser DemonstratioDemonstrationn



Analog Fiber-Optic Transmitter (with Microphone)

Analog Fiber-Optic Receiver(with Audio Power Amplifier)

Speaker5-Meter

Critical Fiber

NOTE: Setup Diagram A on page 90

ProcedureProcedure

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




ProcedureProcedure

Fiber-Optic Communication System - Analog•Laser Laser DemonstratioDemonstrationn



Function Generator200mV peak-to-crestSine Wave

Analog Fiber-Optic Transmitter

LabVIEW Oscilloscope

Analog Fiber-Optic Receiver(with Audio Power Amplifier)

5-Meter

Critical Fiber

Vout

Vin

NOTE: Setup Diagram B on page 91

ProcedureProcedure 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 92 and find the corresponding alphanumeric character




Written AssignmentWritten 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

Written TopicsWritten 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?

Recitation TopicsRecitation 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

ClosingClosing

Return all the equipment back to your instructor

laboratory 10: communication general engineering polytechnic university

Documents

n decimal

binary n

glass n

objectives n

n advantages

diode n

n digitizing

bandwidth n