Laser Communication System Navi

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Sahyadri college of engineering and management

[2012]

LASER COMMUNICATIONSYSTEM

Naveen HE&C


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LASER COMM UNICATION SYSTEM

ABSTRACT:Laser communication is one of the key areas in wireless Communications. This

paper includes analysis, optimization, and design and system level development ofsignal transformation between satellites or any two sources. Which work similarlyto fiber optic links, except the beam is transmitted through free space. While thetransmitter and receiver must require line-of-sight conditions, they have the benefitof eliminating the need for broadcast rights and buried cables. Lasercommunications systems can be easily deployed since they are inexpensive, small,low power and do not require any radio interference studies. The carrier used for

the transmission signal is typically generated by a laser diode. Two parallel beamsare needed, one for transmission and one for reception.

INTRUDUCTION: Laser Communication is one of the emerging area of wirelesscommunication system. Due to its low noise ratio makes its one of the well suitedcommunication medium for exchange of information. Currently laser commutationis adopted in satellite communication for space research activities and due to itsefficiency on low noise ratio, inexpensive, low power and its flexibility and itsresistance to the radio interferences makes laser communication as one of researcharea in wireless communication. In this process, this paper comprises the one such

application of laser communication for information exchange between any twodevices.In Laser Communication the transmitter and receiver must require a line-

of-sight conditions and Laser communications systems have the benefit ofeliminating the need for broadcast rights and buried cables. The carrier used for thetransmission signal is typically generated by a laser diode. Two parallel beams areneeded, one for transmission and one for reception. The optical communicationsystem consists of a transmitter uses a laser beam of a wavelength 650 nm as acarrier in free space.


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Laser communications plays a key role, as a solutions for satisfy everincreasing high demand of bandwidth. In Laser communications systems

bandwidth could be distributed in neighborhoods by putting systems on top ofhomes and pointing them towards a common transceiver with a fast link to the

Internet. It supports possible transmit speeds of up to a gigabit per second, Otherapplications of Laser communications systems technology include temporaryconnectivity needs (e.g. sporting events, disaster scenes, or conventions), or space

based communications.

Space based communication

Laser communication system can be used to transmit sound and data signalsthrough the laser beam of the system. The intensity of the carrier beam changeswith the change in amplitude of the sound signal. Variation in the intensity of the


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laser beam is converted into a variation in the voltage level by using solar panel. Inthis mode of communication the transmitter and receiver requires to satisfying theline of sight conditions. The carrier required for transmission of signal in lasercommunication system is generated by laser diodes.

HARDWARE COMPONENTS REQUIRED :

Transmitter circuit: -IC1 LM386,9V Battery source,C1=100F 25V,LD-1, C2=C3=10 25V,

VR3=22,C4 =0.047F,R1=10, R2= R3=56,

Switch-1.

Receiver circuit: -IC2 LM386,C5=C7=C6= 10F 25V,C8=0.047F, R4=10,

Calculator solar panel,VR4=10K POT,9V Battery source,Switch-2,LD2=Laser diode,Loud speaker 8 0.5W,

EQUIPEMENTS REQUIRED:

potmeter VR1 (10k),

Miltimetre.


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METHODOLOGY

CIRCUIT DIAGRAM - Transmitter:

Fig:1


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CIRCUIT DIAGRAM - Receiver:

Fig: 2


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PROJECT DISCRIPTION:CONSTRUCTION -

The voltage variation on the solar panel is amplified by a low-voltageaudio power amplifier LM386 and reproduced by a speaker. The maximum outputof audio amplifier LM386 is 1 watt, while its voltage gain is 20 to 200. The circuitconsists of a transmitter and a receiver. Both the transmitter and the receiver are

built around IC LM386, powered by a 9V battery.

Fig. 1 shows the transmitter circuit here a laser diode (LD1) withmaximum operating voltage of around 2.6V DC and maximum operating current

of 45 mA is used to transmit the audio signal. The voltage divider networkformed by R2, R3 and VR3 keeps the voltage as well as the current for the laserdiode in the safe region. In place of the laser diode, you can also use a laser

pointer. Remove the battery from the laser pointer. Extend two wires fromterminals of LD1 and connect them to the battery terminals of laser pointer. Thespring inside the laser pointer is the negative terminal. The output power of thelaser pointer is 5 mW. Take care while working with laser, as direct exposure to thelaser beam can be hazardous to your eyes. Point the laser beam to the solar panel.Potmeter VR1 (10-kilo-ohm) is used to change the level of the input audio signal.The audio input (Vin) is taken from the preamplifier output of the music system(CD player, DVD player, etc.). Capacitor C2 and preset VR2 are used to vary thegain of the LM386.

Fig. 2 shows the receiver circuit. The audio signal transmitted by the laserdiode (LD1) is received by the calculators solar panel and amplified by IC2. Thegain of the amplifier is fixed by capacitor C7. Preset VR4 is used to change thesignal level from the solar panel. This signal is fed to input pin 3 of IC2 throughcoupling capacitor C5 so that the DC value from the solar panel can be eliminated.The amplified output from IC2 is fed to the speaker, which plays the music from

the CD player connected at the input (Vin) of IC1.Assemble the transmitter and receiver circuits on separate PCBs and

enclose in suitable cabinets. In the transmitter cabinet, fix two terminals forconnecting the audio signal. Fix switch S1 on the front panel and the laser diode(LD1 or laser pointer) to the rear side of the cabinet. Keep the 9V battery inside thecabinet. In the receiver cabinet, fix the calculatorssolar panel to the rear side such that the transmitted beam directly falls on it. Fix


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switch S2 on the front panel and the speaker to the rear side. Keep the 9V batteryinside the cabinet.

Block diagram of laser communication system

Software: The software is designed to be completely interrupt-driven. Timing isbased around the ability to control an output pin, allowing us to accurately controlthe motor for scanning purposes. The interrupt service routine is called once everyfive microseconds. Upon each interrupt, the program updates its timing counters,reads the output of the analog-to-digital converter when necessary, and performsstate updates for receiver tracking purposes.

The above diagram shows the block diagram of Laser CommunicationSystem, which mainly comprise of 2 sections such as Transmitter section andReceiver section.Transmitter section is used to transmit the data and sound signals, which comprised

by microphone, Conditioning ckt, analog to digital converter and laser diode togenerate medium for transmission of signals. The receiver section is used toreceive the laser beam, using photo transmitter, which incorporated with the data orsound signals from the transmitter comprised of Conditioning, MCR and Digital toAnalog converter to extract the data signals from the received laser beam and given


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as an input to the speaker.

WORKING :

Microphone Amplifier: this is an electric microphone. The microphone

received signals are low power and low signal. For that we are using the LM386op-amp to increase the power and signal.

UART ( universal asynchronous receiver/transmitter) : It is a piece ofhardware that translates data betweenparalle landserial forms.Serial

communication must first be converted back into parallel form by a universalasynchronous receiver/transmitter for increases the speed of the signals.The universal designation indicates that the data format and transmissionspeeds are configurable and that the actual electric signaling levels and methods

typically are handled by a special driver circuit external to the UART.Usually UART hardware generates a start bit, shifts the

required number of data bits out to the line, generates and

appends the parity bit (if used), and appends the stop bits.

A/D:-An analog-to-digital converter (abbreviated ADC, A/D or A to D) is a devicethat converts a continuous quantity to a discrete time digital representation.MCU:The Multipoint Control Unit is an endpoint on the LAN thatprovides the capability for 3 or more terminals and gateways toparticipate in a multipoint conference.

Receiver: A photo detector is optoelectric device that converts the received opticalpower into electrical power with linear response.In most application PIN(positiveintrinsic negative) is the preferred element in the receiver. This is mainly due to thefact that it can be operated from standard power supply, typically between (5-15V); it has lower cost, lower noise, and no gain. A photo diode detects the laser

pulses in a different (distant) location. This signal is put through a comparator inorder to generate solid 5V and 0V values which are applied to the receive pin onthe microcontroller.

DAC:- digital signal to analog converter.

Conditioning: -In psychology, the process of performing some particular action(s)to directly influence an individual's learning; see education (in the broadest senseof the word)
http://en.wikipedia.org/wiki/Hardwarehttp://en.wikipedia.org/wiki/Parallel_communicationhttp://en.wikipedia.org/wiki/Serial_communicationhttp://en.wikipedia.org/wiki/Hardwarehttp://en.wikipedia.org/wiki/Parallel_communicationhttp://en.wikipedia.org/wiki/Serial_communication


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WORKING: when wegive the input like sound or data, Microphone receivesthe data or sound signal. Thissignal coming off the microphone was far too low to

be read by the analog to digital converter. So, for increase the strength of the signalwe pass the signal through the microphone amplifier.Before the signal is putthrough the amplifier, first put the signal through a capacitor to remove DC, andthen through a voltage divider to appropriately bias the signal. The gain is adjusted

by the resistors and for the microphone the gain is around 50-100 (depending on

how much popping and how much quality you want). After, pass the amplifiedsignal into A/D (analog to digital converter) convert the physical signal intodigital (electrical) signal. This digital signal is given to the After the A/D convertertranslates the microphone signal into 8 bits, the MCU generates the appropriate bitsto send (including start and stop bits) and applies them to the laser driver circuit a5V and 0V signals. The BJT in this circuit turns on at 5V and provides the propercurrent according to the diode. Later this signal is passing to UART. Hear signalspeed will increases and this signal is given to conditioning. Data contain signal isthrown into the atmosphere through the laser devise.

A photo diode detects the laser pulses in a different (distant) location. Thissignal is put through a comparator in order to generate solid 5V and 0V valueswhich are applied to the receive pin on the microcontroller. This digital signal isspeed up by the UART. Then signal is received by MCU. That provides thecapability for 3 or more terminals and gateways to participate in a multipointconference. It meansgenerates the appropriate bits to send (including start and stop

bits) and applies them to port. Port is in ordered to get the parallel port support. Itis 8 bit at a time transmission. Its help to transmit the more data signal and itincreases the speed of system. Once this signal is put through the DAC. DACconvert the digital signal into analog signal, also it is boosted and low pass filtered

(to improve sound quality). The result is then fed directly to an audio jack, wherethe signal can be heard using any compatible device.

Comparing the other devise with the laser communication system


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APPLICATIONS:

) In the Laser communications systems bandwidth could be distributed in

neighborhoods by putting laser communication systems on top of homes andpointing them towards a common transceiver with a fast link to the Internet.) with possible transmit speeds of up to a gigabit per second,) with the powerful laser, it would even be possible to communicate usingsatellites to reflect the signals.) It can be used to reproduce sound in large public meetings on open grounds orfor communication between tall buildings. Direct communication between high-

devise Minimum datarate

Maximum datarate

Frequency


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rise buildings in a crowded city would become easy.

ADVANTAGES:

) The advantages of laser communication is that it allows very fast communicationservice between two or more devices than other modes of communications.) It can provide speed more than 1GBps.So it overtakes the LAN or wirelessLAN comprehensively.) Laser communications systems have the benefit of eliminating the need for

broadcast rights and buried cables.) Laser communications systems can be easily deployed since they areinexpensive, small, low power and do not require any radio interference studies.The carrier used for the transmission signal is typically generated by a laser diode.Two parallel beams are needed, one for transmission and one for reception.

) The transmitting and receiving station are smaller and lighter for given range.Less overall power is required for the given distance and data rate. Higher data ratemay be achieved for given distance and power output.

) A tiny light detector may allow for superfast broadband communication overinterplanetary distances. This technology advance offers the space lasercommunication system designer the flexibility to design very lightweight, high

bandwidth, low-cost communication payloads for satellites whose launch costs area very strong function of launch weigh.

) Signals can be reproduced without distortion, even long distances. So thesystem could be used for communication and cable television transmission.

) A one way laser communications system that is capable of the transmissionof both text and sound.x) even by a minute fraction of a degree, the laser will miss by thousands of miles.Instead of better and faster pictures, there could be no pictures.x) Narrow beam divergence

DISADVANTAGES:-

)The noise in photodiodes :The main sources of noise are dark current noise, shot noise and thermalnoise in a photodiode. There is one more source of noise due to random nature ofthe avalanche in an APD. The dark current noise arises due to dark current whichflows in the circuit when the photodiode is in unilluminated environment under

bias condition. It is equal to the reverse saturation current of the photodiode. Themagnitude of this current is strongly dependent on the operating temperature, the


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bias voltage and the type of detector. In an optical receiver, dark current sets anoise floor for the detectable signal power level. Therefore, it should be minimized

by careful device design and fabrication. Dark current in opticaltelecommunication grade Si PIN-photodiodes is typically 100pA, while in Si APDsit is typically 10 pA. In InGaAs based PIN-photodiodes and APDs, the dark currentis of the order of 100nA and it could pose a serious problem unless the device iscooled an appropriate temperature.)Atmospheric Attenuation:- In general, attenuation is the relation betweentransmitted signal power and received signal power as follow10log (dB)Attenuation=10log (P transmitted/Preceived) (db))Optical Receiver Noise :-the internalnoise is created by the opticalreceiver itself such as thermal noise, and dark current noise. Where the thermalnoise current (I t) due to the load resistance (RL) can be calculated by the

following formulaIt= ([4KTBW]/RL) Where t I: is the thermal noise current (Ampere),K: is Boltzmanns Constant,T: is the absolute Temperature (K)BW: is the system bandwidth (Hz) andRL: is the load resistance of the optical receiver ().

v)The free space range lossThe link range loss results from the diverging wave front

Of the optical energy as it traverses the link distance.The calculation of the classical range loss is given byLR=10 log 10 [ /4R] 2

Where:the wave length (nm),Rthe range between 2 things.v)Laser noise.

Conclusion:

This is new wireless technology to transmit the data or soundsignal from one section to other section through the laser beam ofthe system. This system is safety and without radiation.so it is notharm to living beings. The system can likely transmit data andsound much faster than the other system (like 1GB/s). Because ofthis laser communication system became more popular systemthan the other system. The paper firstly analyzed the components of


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maritime laser communication system, the paper made some explanations on thecomponents and functions of the servo system,

REFERENCE:#EFY.com,#E&C Projects,#TECH IN EC.com,#Solar cell & Laser (From Wikipedia, & encyclopedia)#Laser communication.com,#ESA's Space satellite Link Experiment (SILEX) and#The Japanese's Laser Communication Experiment (LCE).

# http://www.seminarprojects.com# The datasheets for all of the parts used are included in the parts section.# 9 out of 10 electrical engineers choose Digikey over any other parts provider.# The others use: Jameco.# The "well written" Mega 32 datasheet.# STK500 datasheet.# ECE 476 Website.
http://www.seminarprojects.com/http://www.seminarprojects.com/

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Laser Communication System Navi