nscsp (proceeding) 2012.pdf

8/10/2019 NSCSP (Proceeding) 2012.pdf

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RESEARCH AND EDUCATION PERSPECTIVE LABORATORYSETUPS IN COMMUNICATION & SIGNAL PROCESSING

Prof. B. Sahu, Prof. J.P. Mishra & Prof. B. Pradhan

Gandhi Institute for Education & Technology Baniatangi, Bhubaneswar- 752060, India

E-mail : [email protected], [email protected], [email protected]

ABSTRACT :

The basis of modern information engineering is the integration of Signal Processing and Communications.Therefore, this subject area of research and education is a complex combination of electrical sciences, electronics& communication and computer science and engineering. Any one module alone will be falling short of realizing thestate of art of the modern data communication and signal processing requirements. A collaged scheme for a usefulresearch and education in the inter-disciplinary area of signal processing and communication is presented here.

Apart from the important depth and breadth subjects, the emphasis of experiments with new trend and state of theart laboratories are listed with required test setups and facilities.

1. INTRODUCTION

The communication and processing of signals areclosely intertwined fields in electrical and computerengineering and together provide the basis of moderninformation engineering. Areas of application are intelephony, broadcast and computer communication,robotic vision, audio and video recording, radar andsonar detection, biomedical signal processing, medicalimaging and remote sensing.

Communication is the process of transferringinformation from one point in time and space toanother point. Signal processing deals with signalrepresentation, as well as signal design and filtering.Therefore, electrical and computer engineering with aspecialty in communication and signal processing findchallenging opportunities world-wide to meet the everincreasing need for new communication and signalprocessing equipment, algorithms and procedureswhich are more convenient, less expensive, and morereliable.

2. BACKGROUND INFORMATION

Samuel B.F. Morse who sent a message over a 10 miletelegraph line was the first to record an electricalcommunication in 1838. Consequently, the subject ofelectrical communication was born. Today we find itcommon place to have telephone conversations fromour automobiles to anyplace in the world. A singleconversation may use wires, radio links, optical fibersand satellite links. Modern communication systemstransfer information at rates more than one billiontimes faster than Morse's first telegraphic message.

Our ability to transfer information in areliable economic manner defines the continued

prosperity of the world. We listen to synthesizedspeech, watch live television from all over the world,communicate with space vehicles dispersed within thesolar system and are able to locate ourselves withoutstanding accuracy using the global positioningsystem (GPS). Future ability to communicate willallow us to reduce our needs for energy by giving usthe ability to work within or near our homes.

Most signal processing systems use bothanalog and digital hardwares. Filtering a signal to

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remove noise, processing an image to sharpen edges orrecognize an object, and speech recognition are alltypical applications of signal processing. Recentadvances in digital hardware have enabled theimplementation of many sophisticated signalprocessing systems at a reasonable cost. Important

examples include the compact disc and speechsynthesis equipments.

3. COMMUNICATIONS, NETWORKING,SIGNAL AND IMAGE PROCESSING

The communications, networking, signal and imageprocessing areas include research directed towards thefollowing :

wireless mobile and PCS communication smart antennas GPS Radar speech recognition and synthesis image processing and pattern recognition print image quality remote sensing local and wide-area computer networks multimedia communication and processing

Results from this area impact how wecommunicate with cellular phones, faxes, and theInternet; the way that we travel using GPS andintelligent highways; and the video, audio, and datathat we receive and transmit for personalentertainment and electronic commerce.

New methods for design, analysis, andoptimization of increasingly complex and demandingcommunication are provided by research in computercommunication networks. Improved switcharchitectures are being developed for high-speedpacket-switched networks that integrate video, voice,and data. Mechanisms for scheduling, bandwidthallocation, error recovery, data compression, andaccess control for local and wide-area computernetworks would provide improved performance andquality of service.

Important results in smart antennas, accurate GPS,improved modems, and efficient radar applications arepossible with the integration of signal processing andcommunications. The new development of narrow-band modem is expected to provide high-performancewireless communication that will be deployed inintelligent transportation systems. Thus, driverlesssmart cars can be seen in the road.

4. INTEGRATION OF SIGNAL PROCESSING(SPS) AND COMMUNICATIONS (COMSOC)SOCIETIES :

Even though the IEEE Signal Processing (SPS) andCommunications (COMSOC) Societies have startedindependently, the technical areas covered by the twosocieties are tightly and undeniably intertwined. Infact, in most problems, it is impossible to tell wherethe signal processing ends and the communications

technology begins, and vice versa. The concept ofrecent advances in cross-layer network design haseffected considerable cross-fertilization between SPSand the communication networks community at theintersection of COMSOC and the Information Theory(IT) Society. The Signal Processing forCommunications and Networking TechnicalCommittee (TC) of SPS is dedicated to exploring andilluminating the connections between these rapidlygrowing fields within the larger IEEE organization.The technical interests include:

Coding, data compression, and information theory Network-distributed signal processing, including

distributed sensing, estimation, detection, coding,and compression

Channel modeling, estimation, and equalization Multiuser, multicarrier, and multiple-access

communications Antenna arrays for wireless communications Synchronization and timing recovery Performance analysis, experimental studies and

measurements Signal processing and cross-layer aspects of ad-

hoc networks, sensor networks, cognitive radioand dynamic spectrum access systems

Cross-layer resource optimization, includingscheduling and queuing protocols

5. SPREAD SPECTRUM COMMUNICATIONTECHNIQUE

It is a digital communication technique thatintentionally expands the bandwidth of a signal fortransmission. Practical applications of spread spectrumtechnology are being made to personalcommunications systems, multimedia networks, anddigital battlefields. These applications are enabled byresearch breakthroughs in coding and modulationtechniques.

6. VIDEO, IMAGE AND SPEECHPROCESSING TECHNOLOGY

The research areas of video, image and speechprocessing technology and their applications includeMPEG video compression for transmission andstorage, print quality enhancement, and featureextraction. The use of image processing techniques inremote sensing is a notable area of research expertise.Speech recognition and synthesis are also active topicsof research. Applications of the results are being made



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to proper name recognition, phoneme recognition, andpitch and lexical stress detection.

7. THE PROGRAM OF RESEARCH ANDEDUCATION

The study of signal processing and communication canbe divided into three parts:(1) The signal processing operations involved in

communication(2) The devices used to perform the signal

processing and communication(3) The underlying physics.

Of necessity, the courses specific to signalprocessing and communication are highlymathematical. The program requires study in circuits,electronics, computers, electromagnetic and controlsystems.

The course consists of four compulsory lecturemodules and four optional modules to be chosen fromtwo streams of application-orientated modules, onestream being in communication engineering and theother in signal processing.

Core modules

Advanced communication theory Advanced data communication Real time signal processing Probability theory and stochastic processes Laboratory Project

Optional modules Coding theory Communication networks Digital Image Processing Distributed computation and networks Information theory Mobile radio communications

Major laboratories in communications andsignal processing research:Communications Research (CR) Laboratory:

Experimental research for the implementation ofalgorithms and architectures for synchronization,equalization, coding, modulation, antenna arrayprocessing, and wireless multiple-access systems. Thefacilities should include programmable signalprocessors, electronic test equipment, satellitecommunication hardware, and commercialcommunication software.

Video and Image Processing (VIP) Laboratory:

Test setups have to be there to display and processhigh-resolution imagery. The provision of multiplesystems should have the capability to digitize, display,and process digital video. A complete suite of videodistribution and editing equipment, a real-time MPEGencoder, and an TM test bed network are theadditional facilities to exit in this laboratory.

Digital Signal Processing (DSP) Laboratory:

It supports research in speech processing, nonlinearDSP, neural networks, design of specialized signals,signal representation, and DSP architectures.

Electronic Imaging Systems (EIS) Laboratory:

The EIS Laboratory should enable research activitiesin the areas of image capture, image rendering, anddocument processing. It should be equipped withhigh-resolution and large format printers, high-precision scanners, and high-performanceworkstations.

Multi Media Test bed (MMT):

MMT is made for the evaluation of networkedmultimedia systems. Research areas supported by thelaboratory include video and image compression,computer networks, multimedia authoring, mediacapture, wireless systems, and a wide variety ofapplications.

8. REFERENCES :

[1] North Dakota State University,www.ece.ndsu.nodak.edu

[2] Paolo Prandoni and Martin Vetterli, SignalProcessing for Communications, University ofMinnesotaMinneapolis, USA

[3] [email protected][4] Imperial College London, South Kensington

Campus, London SW7 2AZ.



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NEAR FIELD COMMUNICATION (NFC) :A TWO WAY CONTACT LESS EXCHANGE OF MORECOMPLEX INFORMATION

Prof. B. Pradhan

Director, GIET, Baniatangi, Bhubaneswar 752060(Former Prof. Mech. Engg., IIT, Kharagpur-721302)

E-mail : [email protected]

ABSTRACT:

Near Field Communication (NFC) is a short-range, standards-based wireless connectivity technology, that uses

magnetic field induction to enable communication between electronic devices in close proximity. Based on RFIDtechnology, NFC provides a medium for the identification protocols that validate secure data transfer. NFC enablesusers to perform intuitive, safe, contactless transactions, access digital content and connect electronic devicessimply by touching or bringing devices into close proximity. It is a form of contactless communication betweendevices like smart phones or tablets. Contactless communication allows a user to wave the smart phone over a NFCcompatible device to send information without needing to touch the devices together or go through multiple stepssetting up a connection. This paper gives an overview of NFC technology, NFC uses and shows some examples.

WHAT IS NFC?

The modern world is ever expanding and with itcomes new technologies that change the way wecommunicate and interact with each other.

Near Field Communication (NFC)technology makes life easier and more convenient forconsumers around the world by making it simpler tomake transactions, exchange digital content, andconnect electronic devices with a touch.

NFC is a set of standards for smart phonesand similar devices to establish radio communicationwith each other by touching them together or bringingthem into close proximity, usually no more than a fewcentimeters. Present and anticipated applicationsinclude contactless transactions, data exchange, andsimplified setup of more complex communicationssuch as Wi-Fi. Communication is also possiblebetween an NFC device and an unpowered NFC chip,called a "tag".

NFC standards cover communicationsprotocols and data exchange formats, and are based onexisting radio-frequency identification (RFID)standards including ISO/IEC 14443 and FeliCa. Thestandards include ISO/IEC 18092 and those defined bythe NFC Forum, which was founded in 2004 byNokia, Philips and Sony, and now has more than 160members. The Forum also promotes NFC and certifiesdevice compliance.

NFC builds upon RFID systems by allowingtwo-way communication between endpoints, whereearlier systems such as contactless smart cards wereone-way only.

HISTORYNFC traces its roots back to radio-frequencyidentification, or RFID. RFID allows a reader to sendradio waves to a passive electronic tag foridentification, authentication and tracking. 1983 (Charles Walton): The first patent associated

with the abbreviation RFID. 2004 (Nokia, Philips and Sony): Established the

NFC Forum. 2006 : Initial specifications for NFC Tags. 2006 : Specification for "Smart Poster" records. 2006: Nokia 6131 was the first NFC phone. 2009: NFC Forum released Peer-to-Peer standards

to transfer contact, URL, initiate Bluetooth, etc. 2010: Samsung Nexus S: First Android NFC

phone . 2011: Google I/O "How to NFC" demonstrates

NFC to initiate a game and to share a contact,URL, app, video, etc.

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2011: NFC support becomes part of the Symbianmobile operating system with the release ofSymbian Anna version.

2011: Research In Motion is the first company forits devices to be certified by MasterCardWorldwide, the functionality of Pay Pass.

2012: EAT, a well known UK restaurant chainand Everything Everywhere (Orange MobileNetwork Operator) partner on the UK's firstnationwide NFC enabled smart poster campaign.(lead by Rene' Bats ford, Head of ICT for EAT,also known for deploying the UK's firstnationwide contactless payment solution in 2008)A specially created mobile phone app is triggeredwhen the NFC enabled mobile phone comes intocontact with the smart poster.

2012: Sony introduces the "Smart Tags", whichuse NFC technology to change modes and profileson a Sony smart phone at close range, included in

the package of (and "perfectly paired" with) theSony Xperia P Smart phone.

WHO BENEFITS FROM NFC?

NFC technology lets smart phones and other enableddevices communicate with other devices containing aNFC tag. Whether swiping our smart phone at thecheckout lane in the grocery store, waving it over adisplay at a local museum, or bumping phones with afriend to share the latest games, near field technologylets we pay, play, and learn easily. Busy mothers checking out at the grocery store. Businessmen and women riding the subway to

work. Businesses looking for faster, more secure

payment methods for customers. Students touring a museum. Access control. Consumer electronics. Healthcare. Information collection and exchange. Loyalty and coupons. Payments. Transport.

NFC TECHNOLOGY

NFC is a set of short-range wireless technologies,

typically requiring a distance of 4cm or less toinitiate a connection. It allows to share smallpayloads of data between an NFC tag and anAndroid-powered device, or between two Android-powered devices.

Simple tags offer just read and write semantics,sometimes with one-time-programmable areas tomake the card read-only. More complex tags offermath operations, and have cryptographic hardware toauthenticate access to a sector. The most

sophisticated tags contain operating environments,allowing complex interactions with code executingon the tag. The data stored in the tag can also bewritten in a variety of formats, but many of theAndroid framework APIs are based around a NFCForum standard called NDEF (NFC Data Exchange

Format).NFC Basics: It describes how Android handlesdiscovered NFC tags and how it notifies applicationsof data that is relevant to the application. It also goesover how to work with the NDEF data in ourapplications and gives an overview of the frameworkAPIs that support the basic NFC feature set ofAndroid.

Advanced NFC: This goes over the APIs that enableuse of the various tag technologies that Androidsupports. When we are not working with NDEF data,or when we are working with NDEF data that

Android cannot fully understand, we have tomanually read or write to the tag in raw bytes usingour own protocol stack. In these cases, Androidprovides support to detect certain tag technologiesand to open communication with the tag using ourown protocol stack.

BLOCK DIAGRAM OF NFC

The analog circuitry handles the modulation anddemodulation of analog signals.

RF level detector detects the presence of anexternal RF field at 13.56Mhz.

UART handles the protocol requirements for the

communication schemes. FIFO BUFFER allows a fast and convenient datatransfer from the host to the UART and viceversa.

MICROCONTROLLER allows autonomousmanagement of communication both on rfinterface and with the host.

HOST INTERFACES are implemented to fulfilldifferent customer requirements.

Fig. 1 NFC block diagram

Advantages

No interference due to decaying fields. Allows communication both between two

powered and passive devices.



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Convenient usage by simply holding the twodevices close to each other.

Disadvantages Data transfer rate is small compared to blue

tooth and other wireless communications. No protection in eavesdropping. No protection in data modification.

ESSENTIAL SPECIFICATIONS

NFC is a set of short-range wireless technologies,typically requiring a distance of 4 cm or less. Itoperates at 13.56 MHz on ISO/IEC 18000-3 airinterface and at rates ranging from 106 kbit/s to 424kbit/s. NFC always involves an initiator and a target;the initiator actively generates an RF field that canpower a passive target. This enables NFC targets totake very simple form factors such as tags, stickers,key fobs, or cards that do not require batteries. NFC

peer-to-peer communication is possible, provided bothdevices are powered.The NFC tags contain data and are typically read-

only, but may be rewriteable. They can be custom-encoded by their manufacturers or use thespecifications provided by the NFC Forum, anindustry association charged with promoting thetechnology and setting key standards. The tags cansecurely store personal data such as debit and creditcard information, loyalty program data, PINs andnetworking contacts, among other information. TheNFC Forum defines four types of tags that providedifferent communication speeds and capabilities interms of configurability, memory, security, dataretention and write endurance. Tags currently offerbetween 96 and 4,096 bytes of memory. As with proximity card technology, near-field

communication uses magnetic induction betweentwo loop antennas located within each other's nearfield, effectively forming an air-core transformer.It operates within the globally available andunlicensed radio frequency ISM band of13.56 MHz. Most of the RF energy isconcentrated in the allowed 7 kHz bandwidthrange, but the full spectral envelope may be aswide as 1.8 MHz when using ASK modulation.

Theoretical working distance with compact

standard antennas: up to 20 cm (practical workingdistance of about 4 cm ) Supported data rates: 106, 212 or 424 kbit/s

NFC Modes:o Passive communication mode: The initiator

device provides a carrier field and the targetdevice answers by modulating the existing field.In this mode, the target device may draw its

operating power from the initiator-providedelectromagnetic field, thus making the targetdevice a transponder.

o Active communication mode: Both initiator andtarget device communicate by alternatelygenerating their own fields. A device deactivatesits RF field while it is waiting for data. In thismode, both devices typically have power supplies.

NFC Codings:

NFC employs two different codings totransfer data. If an active device transfers dataat 106 kbit/s, a modified Miller coding with100% modulation is used. In all other casesManchester coding is used with a modulationratio of 10%.

NFC devices are able to receive and transmitdata at the same time. Thus, they can checkfor potential collisions, if the received signalfrequency does not match with thetransmitted signal's frequency.

APPLICATIONSSome but not all applications examples areshown below:

Fig. 2 connection between electronic devices, accessdigital content and contact less transactions

Fig. 3 Various consumer NFC devices



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Fig. 4 An NFC-enabled mobile phone interacting witha Smart Poster

Fig. 5 A ticket stamping machine of the AustrianFederal Railways that can be used to purchase mobiletickets ("Handy-Ticket").

Fig. 6 Search for availability of tickets

NFC-enabled handsets

In 2011, handset vendors released more than 40 NFC-enabled handsets; Google, includes NFC functionalityin their Android mobile operating system and providesa NFC payment service, Google Wallet.

Deployment

As of April 2011, several hundred NFC trials havebeen conducted. Some firms have moved to full-scaleservice deployments, spanning either a single countryor multiple countries. Multi-country deploymentsinclude NFC technology to banks, retailers, transport,and service providers.

NFC IN COMMERCE:

NFC devices can be used in contactless paymentsystems, similar to those currently used in credit cardsand electronic ticket smartcards, and allow mobilepayment to replace or supplement these systems. Forexample, Google Wallet allows consumers to storecredit card and store loyalty card information in avirtual wallet and then use an NFC-enabled device atterminals that also accept MasterCard Pay Passtransactions. Germany, Austria, Finland, New Zealandand Italy have trialled NFC ticketing systems forpublic transport. China is using it all over the countryin public bus transport and India is implementing NFCbased transactions in box offices for ticketingpurposes.

USES OF NFC (SUMMARY):

Access Control: Replacing traditional keys foreither physical access (hotel room) or control(starting a car)

Ticketing: Replacing paper tickets for socialevents and public transportation

Contactless Payments: Mobile payments debitedfrom financial or MNO linked accounts

Interactive World: Marketing and exchange ofinformation such as schedules, maps, businesscard and coupon delivery using NFC Marketingtags

Media Sharing: Transfer images, videos, musicbetween mobile phones

Social media e.g. "Like" on Face book, "Follow"on Twitter via NFC smart stickers in retail stores

NFC IN CONJUNCTION WITH BLUETOOTHAND WI-FI CONNECTIONS

NFC offers a low-speed connection with extremelysimple setup, and can be used to bootstrap more

capable wireless connections. An example of this is inGoogle's Mobile Phone OS Android 4.1. In order toachieve a file transfer over Android Beam (an NFCsharing service), the software automatically completesthe steps of enabling, pairing and establishing aBluetooth connection when doing a file transfer viaAndroid Beam. The same principle can be applied tothe configuration of Wi-Fi networks.



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COMPARISON WITH BLUETOOTH

NFC and Bluetooth are both short-rangecommunication technologies that are integrated intomobile phones. NFC operates at slower speeds thanBluetooth, but consumes far less power and doesn'trequire pairing.NFC sets up faster than standard Bluetooth, but is notfaster than Bluetooth low energy.

NFC IN SOCIAL NETWORKING:

NFC can be used in social networking situations, suchas sharing contacts, photos, videos or files, andentering multiplayer mobile games.

NFC IN IDENTITY DOCUMENTS:

The NFC Forum promotes the potential for NFC-enabled devices to act as electronic identity documentsand keycards. As NFC has a short range and supportsencryption, it may be more suitable than earlier, lessprivate RFID systems.

STANDARDIZATION BODIES

NFC was approved as an ISO/IEC standard onDecember 8, 2003 and later as an ECMA standard.ISO/IEC 18092 / ECMA-340

Near Field Communication Interface andProtocol-1 (NFCIP-1)

ISO/IEC 21481 / ECMA-352 Near Field Communication Interface andProtocol-2 (NFCIP-2)

GSMA

The GSM Association (GSMA) is the global tradeassociation representing nearly 800 mobile phoneoperators and more than 200 product and servicecompanies across 219 countries. Many of its membershave led NFC trials around the World and are nowpreparing services for commercial launch.

NFC FORUM

The NFC Forum is a non-profit industry associationformed on March 18, 2004, by NXP Semiconductors,Sony and Nokia to advance the use of NFC short-range wireless interaction in consumer electronics,mobile devices and PCs. The NFC Forum promotesimplementation and standardization of NFCtechnology to ensure interoperability between devicesand services. As of March 2011, the NFC Forum had135 member companies.

OTHER STANDARDIZATION BODIES

Other standardization bodies that are involved in NFCinclude: ETSI / SCP (Smart Card Platform) to specify the

interface between the SIM card and the NFC

chipset. Global Platform to specify a multi-applicationarchitecture of the secure element.

EMVCo for the impacts on the EMV paymentapplications

SECURITY ASPECTS

NFC offers no protection against eavesdropping andcan be vulnerable to data modifications. Applicationsmay use higher-layer cryptographic protocols (e.g.,SSL) to establish a secure channel.

KEY BENEFITS OF NFCNFC provides a range of benefits to consumers andbusinesses, such as: Intuitive : NFC interactions require no more than

a simple touch Versatile : NFC is ideally suited to the broadest

range of industries, environments, and uses Open and standards-based : The underlying

layers of NFC technology follow universallyimplemented ISO, ECMA, and ETSI standards

Technology-enabling : NFC facilitates fast andsimple setup of wireless technologies, such as

Bluetooth, Wi-Fi, etc.) Inherently secure : NFC transmissions are short

range (from a touch to a few centimeters) Interoperable : NFC works with existing

contactless card technologies

CONCLUSIONThis presentation offers insightful information thatkeeps us informed on both the benefits and possibledrawbacks of NFC technology.

We look at this emerging technology fromthe point of view of both the individual consumer

interested in how near field communication can makethe life easier and also from the point of view ofbusinesses both large and small considering theincorporation of near field communication technologyinto their stores. Whether for profit or personal use, wecan find ways that near field communication can proveuseful in helping the customers or accomplishing ourown shopping needs faster.



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Some specific observations are as follows: Providing secure channel will avoid the draw

backs such as evesdropping or datamodification.

NFC is compatible with existing RFIDinfrastructures.

NFC is an efficient technology forcommunications with short ranges

REFERENCES

1. Ortiz, C. Enrique (2006-06). "An Introduction toNear-Field Communication and the ContactlessCommunication API".http://java.sun.com/developer/technicalArticles/javame/nfc/.

2. Kasper, Timo; Dario Carluccio, Christof Paar (2007). "An embedded system for practicalsecurity analysis of contactless smartcards"(PDF).Springer LNCS (Workshop in InformationSecurity Theory and Practices 2007, Heraklion,Crete, Greece) 4462: 15060.

http://www.crypto.rub.de/imperia/md/content/texte/publications/conferences/embedded_system.3. http://en.wikipedia.org/w/index.php?title=Near_fi

eld_communication&oldid=5158638964. http://www.seminarsandppt.com5. Wikipedia, the free encyclopedia6. "What is NFC?". NFC Forum. http://www.nfc-

forum.org/aboutnfc/.7. " ". . :// .

. / /.



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A FULL DUPLEX FIBER OPTICAL CATV TRANSPORTSYSTEMS EMPLOYING REFLECTIVE SEMICONDUCTOR

OPTICAL AMPLIFIER

A. S. Patra 1 Haldia Institute of Technology, Haldia, India

Email: [email protected]

ABSTRACT:

A full duplex directly modulated fiber optical CATV transport system employing a reflective semiconductor opticalamplifier (RSOA) as wavelength reuse and remodulation schemes is proposed and demonstrated. Impressive

performances of downstream carrier-to-noise ratio (CNR)/composite second-order (CSO)/composite triple beat(CTB) were achieved accompanied with acceptable upstream CNR/CSO/CTB values, over a 40-km single-mode

fiber (SMF) transmission. The proposed full duplex directly modulated transport systems are simpler than theconventional externally modulated ones.

1. INTRODUCTIONThe first large scale commercial application of analog fiberoptic links was the distribution of CATV signal. High video

quality requirement of fiber AM-VSB 80-channel CATVtransport systems has becoming widespread throughout thecable industry [1]. The acceptable transmission performanceof fiber optical CATV systems by cascading erbium-dopedfiber amplifiers (EDFAs) is limited by the parameters such asCNR, CSO, and CTB. Several approaches have beenproposed to improve the overall performances of fiber opticalCATV transport systems. However, sophisticated sidebandfiltering and external light injection locking techniques [2],[3]; as well as expensive dual electrode Mach-Zehndermodulator (MZM) and phase modulator [4], [5] are required.Direct modulation of a distributed feedback laser diode (DFBLD) has therefore become attractive for lightwave transportsystems, because it costs lower compared with an externallymodulated transmitter. In recent studies, RSOA has beenused as wavelength reuse and remodulation schemes in fullduplex wavelength-division-multiplexing passive opticalnetwork and radio-over-fiber systems [6], [7]. But, itsapplication in analog lightwave transport systems has notbeen reported. RSOA, which has wavelength reuse andremodulation characteristics, is expected to have goodperformances in full duplex directly modulated fiber opticalCATV transport systems. In this paper, an architecture of a

full duplex directly modulated fiber optical CATV transportsystem employing a RSOA to remodulate the upstreamCATV signal is proposed and demonstrated. To the best of

our knowledge, it is the first time to transmit full duplexCATV signals employing a RSOA as wavelength reuse andremodulation schemes. In contrast to the full duplexexternally modulated fiber optical CATV transport systems,good performances of downstream CNR/CSO/CTB wereobtained accompanied with acceptable upstreamCNR/CSO/CTB values, over a 40-km single-mode fiber(SMF) transmission.

2. EXPERIMENTAL SETUPFig. 1 shows two full duplex AM-VSB 77-channel fiberoptical CATV transport systems based on a RSOA aswavelength reuse and remodulation schemes. Fig. 1(a)(referred to as system I) shows the full duplex externallymodulated CATV transport systems. Fig. 1 (b) (referred to assystem II) shows our proposed full duplex directly modulatedCATV transport systems. The output power and noise figureof each EDFA used in systems I and II are ~17 dBm and ~4.5dB, at an input power of 0 dBm, respectively. In system I,channels 2-78 generated from a multiple signal generator(MATRIX SX-16) were fed into an externally modulatedtransmitter with an optical modulation index (OMI) of ~3.5%per channel. In system II, a total of 77 carriers from a

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multiple signal generator were directly fed into the DFB LD,with a central wavelength of 1550.52 nm)( and an OMI of3.5% per channel. Light is injected in the counter-propagation direction through an optical isolator, an opticalcoupler, and a polarization controller. System link with atransmission length of 40 km SMF length; to transmit opticalsignal over a 40-km SMF link, the optical power wasamplified by the EDFA-I. The variable optical attenuator(VOA) was introduced at the start of the optical link, thiswould have resulted in less distortions since the opticalpower launched into the fiber would have been less andseeded into the RSOA would have been optimized. Next tothe VOA, an optical circulator (OC) was placed to bridgeboth downstream and upstream signals. Over a 40-km SMFtransmission, the downstream signal was split by a 12optical splitter. One half of the signal was received by anoptical receiver, and the other half was circulated and reusedby the OC and RSOA. As to up-link transmission, a RSOAwith 1.5 GHz modulation bandwidth is placed at the

receiving site to reuse the optical wavelength and remodulatethe CATV signal.

Fig. 1. (a) The full duplex externally modulated CATVtransport systems based on a RSOA

Fig. 1. (b) Our proposed full duplex directly modulatedCATV transport systems based on a RSOA

The optical signal is circulated and amplified by the OC2 andthe EDFA-II before coupled into the same 40 km SMF link.Since both of the downstream and upstream signals aretransmitted at the same SMF, an optical isolator is placednext to the EDFA-II to avoid the downstream signal. CNR,CSO and CTB values were measured and analyzed at bothsites by HP-8591C CATV analyzer.

3. EXPERIMENTAL RESULTS

Injection locking scheme is employed in system II, one keyfeature of injection locking is that the injected laser is forcedto oscillate at the injection frequency instead of the originalfree-running frequency. Therefore, the frequency componentat the injection frequency becomes dominant. The injectionlocking behavior happens when an injection laser)'( isslightly detuned to wavelength longer than that of theinjected laser )( . As is injection-locked, its opticalspectrum shifts a slightly longer wavelength to' . Thewavelength of the injected light (' , 1550.64 nm) must becarefully chosen to ensure that the optimal enhancement inthe frequency response of DFB LD is obtained. The optimalinjection locking condition is found as the detuning between and ' is 0.12 nm ( ' = 0.12 nm). The simplest methodto convert electrical signal into optical one is by directlymodulating the DFB LD, while the direct modulation of aDFB LD is limited by the inherent frequency response.

Overcoming the limitation would provide an effectiveapproach of transmitting CATV signals. The gain model ofSOA which explains the gain saturation phenomenon is givenby [8]:

out inin

out

PPG

PP

G / 10

+== (1)

Where,G0 is the unsaturated gain,Pin is the input opticalpower, andPout is the output optical power. To define thesaturation optical powerP sat, at that power in which gainreducing to half of the G0. The output power (P R, out ) andoptical gain (G R) of RSOA can be expressed as:

in Rout R P RGP2

, = (2)

in

insat insat insat

R RP

PP RGPPPP

G 24)()( 02 ++++

= (3)

Where R is the reflectivity. It is obvious that, from equations(2) and (3), theP R, out and G R depend on theP in; higherP in leads to higherP R, out and lowerG R. It is a transmission over a SMF using the same wavelengthsin both directions; it may happen that Rayleighbackscattering noise limits the systems seriously. TheRayleigh backscattering noise is generated due to both theback-reflection of downstream signal and that of remodulatedupstream signal in a RSOA. To reduce the Rayleighbackscattering noise caused by the remodulation, the RSOAis operated in the saturation region. Fig. 2 shows themeasured CSO and CTB values (CH78; the highest channel)for up-link transmission by varying the RSOA injectionpower level from -10 to -30 dBm; in other words, from thelinear region to the saturation one. As the injection powerinto the RSOA increased, the reflection tolerances of both theupstream and downstream CATV signals were improved tosome extent. This was mainly due to the fact that the RSOAgain was reduced as the injection power increased, andconsequently the power ratio of the reflected light (upstream)to the signal light (downstream) was reduced. The higher theinjection power into the RSOA, the more suppressed the


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downstream CATV signal in the upstream transmissionbecome, finally improving the CSO and CTB performancesof upstream CATV signal.

Fig. 2. The measured CSO and CTB values (CH78) for up-link transmission by varying the RSOA injection power level.

Fig. 3(a), (b) and (c) show the measured CNR, CSO and

CTB values as RSOA with -10 dBm injection power underNTSC channel number for systems I and II, respectively. Itcan be seen that the downstream CNR/CSO/CTB values(51.4/65.2/65.1dB) of systems I and II are almost identical,and the upstream CNR/CSO/CTB values (50.2/60.2 /60 dB)of systems I and II are almost the same. In general, if oneuses a directly modulated 1.55-m laser transmitter fortransmission, the transmission distance is limited to only afew tens of kilometers. To achieve a long-haul transmissionat 1.55m, externally modulated transmitter should be used.However, since the transmission distance is limited in thisstudy, the down/up-link performances of system II are similarto those of system I. It also can see that, from Fig. 3(a), (b)and (c), the upstream CNR/CSO/CTB values are degraded

about 1.2/5/5.1 dB, compared to the downstream ones. Theupstream CNR degradation is mostly due to the amplitudefluctuation from backscattering and additional relativeintensity noise from the RSOA. And further, the upstreamCSO and CTB deteriorations can be mainly attributed to theRayleigh backscattering noise caused by the remodulation.Originally, the downstream CATV signal should be erased bythe RSOA. With the elimination of the downstream CATVsignal, the upstream CATV signal is remodulated by theRSOA. Nevertheless, the downstream CATV signal is notsufficiently suppressed, in which leading to distortions forupstream CATV signal.

Fig. 3. The measured (a) CNR, (b) CSO and (c) CTB valuesunder NTSC channel number for systems I and II.

4. CONCLUSIONSA full duplex directly modulated fiber optical CATVtransport system employing a RSOA at the receiving site isproposed and demonstrated. Impressive transmissionperformances of downstream CNR/CSO/CTB were obtainedaccompanied with acceptable upstream CNR/CSO/CTBvalues. It reveals a prominent one with simpler advantage

than that of externally modulated transport systems. Ourproposed architecture is suitable for the full duplex fiberoptical CATV transport systems in limited transmissiondistance.

REFERENCES

[1] H. Gebretsadik, H. T. Foulk, N. C. Frateschi, W. J. Choi,S. V. Robertson, and A. E. Bond, Linearised integratedSOA-EA modulator for long-haul and FTTH CATVapplications at 1.55m, Electron. Lett ., 40, 1016 (2004).[2] S. J. Tzeng, H. H. Lu, C. Y. Li, K. H. Chang, and C. H.Lee, CSO/CTB performance improvement by using Fabry-Perot etalon at the receiving site,Progress In

Electromagnetics Research Lett. , 6, 107 (2009).[3] H. H. Lu, A. S. Patra, S. J. Tzeng, H. C. Peng, and W. ILin, Improvement of fiber optical CATV transport systemsperformance based on lower- frequency side mode injection-locked technique, IEEE Photon. Technol. Lett., 20 , 351(2008).

(a)

(c)

(b)


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DETERMINATION OF OPTIMUM ANGLE OF ROTATION OF COILFOR PROCESSING MAGNETIC RESONANCE SIGNALS

1Prof. (Dr.) R P Das, 2Prof. P. Deepthi1Principal,2Asst. Professor

1,2 Pydah college of engineering and technology

ABSTRACT

This paper presents a study on LOW COST MAGNETIC RESONANCE ANALYZER which help the medicalspecialists and study the various kinds of body tumors , cancers etc by studying the blood properties using magnetic resonance principle. The emphasis on the rotation of coil around with the sample .

Key words - Proton magnetometer ,Magnetic resonance imaging , proton procession ,T1 , T2 parameters ,radiotransmitters.

1. INTRODUCTION

Conventional MAGNETIC RESONANCEIMAGING SCANNER is a more popular device used

in the field of biomedical imaging for detection oftumors , cancers, and for other tissue related studies .They use powerful magnetic fields for scanningpurpose . Though they have not been demonstrated tocause the direct biological damage ,they suffer frommany mentioned limitations as follows :

These conventional MRIs cannot be usedscanning the people who are using SURGICALPARTS within their body .

They cannot be used for the people who are usingPACE - MAKERS within their heart .

Apart from the above technical disadvantages ,HIGH INSTALLATION AND HIGHSCANNING COST is the major drawback whichis making these MRIs an unaffordable one for awide range of people in many countries .

In this method , blood is to be tapped from suspectedarea and would be put in a small containersimultaneously for the application of magnetic pulse sothat the effect of proton procession can be

electronically recorded . Basically , protons havingquantized spin angular momentum process about thedirection of the magnetic field . In resonance the

energy of the system can be changed by an externalinfluence (small alternating magnetic field ) arrangedat various angles with respect to the main field ,resultant field moves between the limits defined by which is quiet small . By selecting optimum sampleand verifying the frequency and angle of application anumber of useful parameters can be obtained aroundresonance condition.

2 . PRINCIPLE OF OPERATIONHuman blood flow can be compared to a running watersystem which passes through impure (55%

plasma)/polluted areas maintaining average purityunder quasi laminar flow conditions .Dependingupon the instantaneous bed over which fluid flowsthere could be some tangible change in properties orcharacteristics . This is also analogous to the case oftransformers in which cooling oil flows through thesystem and depending on the localized defects , thecharacteristics of oil changes from which the defects ofthe system can be defected . In proton magnetometer


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used for geological applications a small bottle of wateror alcohol is taken and a magnetic coil is wound over itfor creating the resonance signal of the protonprocession .

Fig : -1 PRINCIPLE OF OPERATION

All these suggest that this experiment will besuccessful in developing a low cost system fordetection of tumor and allied elements . Some

researcher have worked on such vascular technologiesbut again used heavy magnetization . In the proposedsystem , based on variation of angle and type ofvoltage , a number of parameters will be found incontrast to conventional device . The 90 RF field willbe actually replaced by optimum signal capable ofgenerating more parameter . The effective creativepart of the system is localized sampling of blood fromsusupected areas coupled with simultaneousapplication of low level magnetization so theinstaneous proton procession effects can be recordedanalyzed by using cuff technique as in normal BP

measurement , blood flow can be restricted to certainareas and static measurement cab be taken . Thesemethods are likely to reflect the issue condition betterincluding case of cervical cancer .

As the human body contains nearly 80% ofwater , it forms a good sample for magnetic resonance .The basic molecular magnets in the body donot showany magnetism in the normal condition . When thebody or part of the body is subjected to a staticmagnetic field , magnetic polarization occurs as infig 2 . In the large system whole human body isexposed to the magnetism influence . In our setup weare only considering a portion of the body or even thesample of fluid taken from the body from the suspectedareas.

The transformation from the random state topolarized state takes some time , the time constant ofwhich is calledspin lattice relaxation time of waterprotons. Water present in different tissues (refelected

by blood) may have different values of this timeconstant T1 . Such variation shows that from nerves toflesh there is a variation of 80 % to 20 % in watercontent( muscles 70% liver 65% skin 62% ).Distribution of proton T1 values [3] have been reported

also :- muscles 1000ms , skin - 600ms , liver 500ms.

The magentisation vector of the staticmagnetic field can be rotated by 90 or 180 by theapplication of appropriate RF pulse . For field strengthof one tesla , the RF pulse can be set around 40 MHz 42 MHz. The macroscopic magnetization growsexponentially towards the equilibrium values s hown infig-3 . This variation leads to decay signal (called FreeInduction Decay) in to coil placed in a certain direction. The decay constant gives the spin spin relaxationtime T2 which is used for spin echo as this shown is fig-4.

Fig -3 RESULTANT MAGNETIZATION INSTATIC FIELD .

Fig - 4 FREE INDUCTION DECAY


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RESONANCE AND FOURIER TRA

Consider two samples A and B subjectsteady magnetic field [4] having resongiven by 2 f 0 = B0 .If a linearly varyingfield) is supermind so that then thesample has B1 < B0 and in the 2nd samas shown in fig -5 . So in the first caseforce at f 1 < f 0 and in the second onesignals have fourier transformation githe amplitude of peaks is directly prowater content and frequency of separatito the gap between the two samples. Bycan we can encode spatial informatiosignal which leads to spin density imvariation of water content .

fig -5 :- GRADIENT SUPERPOSITIO

The amptitude of the peaks isthe protons T1 values . A special(Inversion recovery ) can be usexperimentation giving scope to T1

.Instead of two samples , we may consisites on the gradient leading to m psignal which can be converted intointensity variation . These can be exdimensions and total imaging can be ach

EXPERIMENTAL APPARATUS

The basic idea of proton magnetometerfor our study .In this setup a sample owater) can be kept in a container arouis wound . The oscillator creates the RThe magnetization pulse is picked upcoil and amplified by instrumentashowing in fig-6 . The decay of the

studied in oscilloscope pr any recordinadvantages of this apparatus that it canthe magnetic field at all possible avarious patterns of study .

SFORMS

ed to the sameance frequencyfield (gradientluid in the 1st le has B2 > B1 esonance takesat f 2 > f 0 . FIDve two peaks ,ortional to then proportional

this method weinto the FID

ging based on

proportional toulse sequenced for suchased imaging

der m- protonsints amptitudean m pointtended to 3 ieved.

has been usedfluid (blood,

d which a coilfield required.

by the sensingtion amplifier

pulse can be

g device . Thesuitably rotatengles creating

Fig 6 OSCILLATORCIRCUITS

RESULTS/ CONCLUSION

Optimisation of coil position isfeature . In normal cases , such va90 or 180 . Our resonance result, 105 & 165 .Of these the maxiclose to 105 .Second observation has been th

capable of generating T1 & T2 pattwithout heavy investments on thevariation with respect to T1 wasvalues determined by the convvariation T2 was more rotation amaximum variation by15%) .With such low level variation of 1& T2 , this proton magnetometerapproach to magnetic resonance imREFERENCE

[1] K C Li .& M D Bednanski ,imaging using MRI , IEEInternational Symposium and Bio

Pp 809 -910, 2002 .[2] R P Das , LOW COSTconference on Instrumentation at A

ND AMPLIFIER

the most importantriation is limited tos were setup for 75mization took place

at this analyser is

rn of similar natureagnetic setup . Thewithin 10% of thentional setup .The

ngle dependent( the

0% and 15% for T1offers an alternativeaging

Vascular targetedE proceedings onedical imaging ,

MRI , NationalBIT ,cuttack 2006


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OPTICAL FIBER COMMUNICATIONAN OVERVIEW

1Prof. S.N. Padhi, 2Debashis Panda 1 HOD & Associate Professor, Department of ECE, GIET, Gunupur

27 th semester ECE, GIET, Gunupur

ABSTRACT

This paper deals with the historical development of optical communication systems and their failures initially. Thenthe different generations in optical fiber communication along with their features are discussed. Some aspects of totalinternal reflection, different types of fibers along with their size and refractive index profile, dispersion and lossmechanisms are also mentioned. Finally the general system of optical fiber communication is briefly mentioned alongwith its advantages and limitations. Keywords. Bandwidth; optical fiber; group index; group velocity; v-number;

INTRODUCTION

Optical fiber communication plays a vital role in thedevelopment of high quality and high-speedtelecommunication systems. Today, Optical fibers arenot only used in telecommunication links but also usedin the Internet and local area networks (LAN) toachieve high signaling rates.

Table 1 shows the different communication systemsand their bit rate distance product. Here the repeaterspacing is mentioned as distance.

Table 1. Bit rate distance product.

System Bit rate distanceproduct (bit/s) - km

Old opticalcommunication

1

Telegraph 10

Telephone 103

Coaxial cables 105

Microwaves 106

Laser light in open air 109

Different types of fibers:

A typical glass fiber consists of a central core glass (50m) surrounded by a cladding made of a glass ofslightly lower refractive index than the cores

refractive index. The overall diameter of the fiber isabout 125 to 200 m. Cladding is necessary to provideproper light guidance i.e. to retain the light energywithin the core as well as to provide high mechanicalstrength and safety to the core from scratches. Basedon the refractive index profile we have two types offibers (a) Step index fiber (b) Graded index fiber.(a) Step index fiber : In the step index fiber, therefractive index of the core is uniform throughout andundergoes an abrupt or step change at the core claddingboundary. The light rays propagating through the fiberare in the form of meridional rays which will cross thefiber axis during every reflection at the core claddingboundary and are propagating in a zig-zag manner asshown in figure.(b) Graded index fiber : In the graded index fiber, therefractive index of the core is made to vary in theparabolic manner such that the maximum value ofrefractive index is at the centre of the core. The lightrays propagating through it are in the form of skewrays or helical rays which will not cross the fiber axisat any time and are propagating around the fiber axis ina helical (or) spiral manner as shown


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Mode is the mathematical concept of describing thenature of propagation of electromagnetic waves in awaveguide. Mode means the nature of theelectromagnetic field pattern (or) configuration alongthe light path inside the fiber.(c) Single mode fibers : In a single mode fiber, onlyone mode can propagate through the fiber. Normallythe number of modes propagating through the fiber is

proportional to its V-number where

Here a = radius of the core of the fiber;n1 = refractive index of the core,= wavelength of light propagating through the fiber;

= relative refractive index differenceIn the case of single mode fiber, V-number_ 2.405.The single mode fiber has a smaller core diameter (10

m) and the difference between the refractive indicesof the core and the cladding is very small. Fabricationof single mode fibers is very difficult and so the fiber is

expensive. Further the launching of light into singlemode fibers is also difficult. Generally in the singlemode fibers, the transmission loss and dispersion ordegradation of the signal are very small. So the singlemode fibers are very useful in long distancecommunication.(d) Multimode f ibers : Multimode fibers allow a largenumber of modes for the light raystraveling through it. Here the V-number is greater than2.405. Total number of modes N propagating througha given multimode step index fiber is given by

whered is the diameter of the core of the fiber. For amultimode graded index fiber having parabolicrefractive index profile core,

which is half the number supported by a multimodestep index fiber. Generally in multimode fibers, thecore diameter and the relative refractive index

difference are larger than in the single mode fiber. Inthe case of multimode graded index fiber, signaldistortion is very low because of self-focusing effects.Here the light rays travel at different speeds in differentpaths of the fiber because of the parabolic variation ofrefractive index of the core. As a result, light rays near

the outer edge travel faster than the light rays near thecentre of the core. In effect, light rays are continuouslyrefocused as they travel down the fiber and almost allthe rays reach the exit end of the fiber at the same timedue to the helical path of the light propagation.Launching of light into the fiber and fabrication of thefiber are easy. These fibers are generally used in localarea networks.

Basic optical fiber communication system

Figure shows the basic components in the optical fibercommunication system. The input electrical signalmodulates the intensity of light fromthe optical source.The optical carrier can be modulated internally or

externally using an electro-optic modulator (or)acoustooptic modulator. Nowadays electro-opticmodulators (KDP, LiNbO3 or beta barium borate) arewidely used as external modulators which modulate thelight by changing its refractive index through the giveninput electrical signal. In the digital optical fibercommunication system, the input electrical signal is inthe form of coded digital pulses from the encoder andthese electric pulses modulate the intensity of the lightfrom the laser diode or LED and convert them intooptical pulses. In the receiver stage, the photo detectorlike avalanche photodiode (APD) or positive-intrinsicnegative (PIN) diode converts the opticalpulses into electrical pulses. A decoder converts the

electrical pulses into the original electric signal

Advantages of optical fiber communication

1. Wider bandwidth :2. Low transmission loss :3. Dielectric waveguide 4. Signal security :5. Small size and weight :

Transmission losses in fibers

The transmission loss or attenuation of the signal in anoptical fiber is a very important quantity to consider inoptical fiber communication. The attenuation of thesignal transmitting through the fiber results fromabsorption and scattering and is measured in


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decibel/km and is a function of wavelength as shown infigure.The optical communication wavelengths are 0.8, 1.3and 1.55 m. Attenuation can be classified into twotypes:

(i) Intrinsic losses and (ii) Extrinsic losses.Mechanisms generating intrinsic losses1. Tail of infrared absorption by Si-O coupling.2. Tail of ultraviolet absorption due to electron

transition.3. Rayleigh scattering due to spatial fluctuation of

refractive index and is inversely proportional to44. Absorption by molecular vibration of OH

impurity5. Absorption by transition metal impurities like Cr, V,

Fe, Mn and Ni.

Thus it is found that in the case of pure silica fibers thetransmission losses are reduced to a minimum value at1.55 m wavelength. At 1.3 m also, the transmissionlosses are minimum but the net attenuation is slightlygreater with respect to the wavelength 1.55m.

Mechanisms generating extrinsic losses:

1. Geometrical non-uniformity at the core-claddingboundary.

2. Imperfect connection or alignment between fibers.3. Microbending.4. Radiation of leaky modes.

Extrinsic losses are very small when compared tointrinsic losses and can be minimized by proper careduring the manufacturing and installation of the fibers.

Different components used in the optic fibercommunication systems

Optical sources

Heterojunction LEDs and lasers are mostly used as theoptical sources in optical fiber communication. Hetero- junction means that a p-n junction is formed by a singlecrystal such that the material on one side of the junction differs from that on the other side of the junction. In the modern GaAs diode lasers, a hetero junction is formed between GaAs and GaAlAs. Thistype of p-n junction diode laser or LED is used at 0.8

m wavelength. At longer wavelengths, InP-InGaAsPheterojunction laser diodes are used. Heterojunctionlasers or LEDs are superior to conventionalhomojunction lasers or LEDs. Generally heterojunctionlasers and LEDs have minimum threshold currentdensity (10 A/mm2), high output power (10 mW) evenwith low operating current (


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where M is called avalanche multiplication whichisgreater than 50. APDs are made from silicon orgermanium having operating wavelength 0.8m andfrom InGaAs having operating wavelength 1.55m.

Optical fiber communication

Optical amplifiersIn the long distance optical fiber communicationsystems, the repeaters are situated at an equal distanceof 100 km. These are used to receive and amplify thetransmitted signal to its original intensity and then it ispassed on to the main fiber. Previously it was done byconversion of optical energy into electrical energy andamplification by electrical amplifiers and thenreconversion of electrical energy into optical energy.Such methods not only increase the cost andcomplexity of the optical communication system butalso reduce the operational bandwidth of the system.But today it is done by erbium doped optical fiberamplifiers in an elegant manner by inserting a length of10 m fiber amplifier for every 100 km length of mainfiber. By this, the signal to noise ratio is greatlyimproved due to optical domain operation only .

Fiber couplers

A coupler is a device which distributes light from amain fiber into one or more branch fibers. There arecore interaction type couplers and surface interactiontype couplers. In core interaction type couplers, thelight energy transfer takes place through the core cross-section by butt jointing the fibers or by using someform of imaging optics between the fibers (i.e. usinglensing schemes such as rounded end fiber, a sphericallens used to image the core of one fiber on to the corearea of the other fiber and a taper-ended fiber). In thesurface interaction type the light energy transfer takesplace through the fiber surface and normal to the axisof the fiber by converting the guided core modes tocladding and refracted modes.

Different types of fibers couplers and their functions

(i) Three and four port couplers : Figures 5a and 5bshow the uses of a three port coupler as splitter andcombiner of the signals. Light from the input fiber iscoupled to the output fibers as shown in figure 5a orthe light from the branch fibers are combined to form asingle input to the output fiber. For splitting, a singleinput fiber core is situated between the cores of twooutput fibers. This is called the lateral offset method. Inthis method, the input power can be distributed in awell defined proportion by appropriate control of theamount of lateral offset between the fibers.Figure shows the directional coupler which is a fourport coupler. In this coupler, the fibers are generallytwisted together and then spot fused under tension suchthat the fused section is elongated to form a biconicaltaper structure. It can act as a three port coupler (or) T

coupler if one of the input ends (or) one of the outputends is closed. As shown infigure, each port is meantfor different functions.

Figure 5. (a) Three port coupler as a splitter. (b) Threeport coupler as a combiner.

Figure 6. Four port coupler.

Inputs

C - to pass the main signal into the main fiber.A - to combine the extra signal or data into the main

fiber.OutputsD - to transmit the combined signal (or) remaining

portion of the main signal throughthe main fiber.B - to collect the split signal.This type of coupler is based on the transfer of energyby surface interaction between the fibers. The amountof power taken from the main fiber or given to themain fiber depends on the length of the fused section ofthe fiber and the distance between the cores of thefused fibers. This can also act as a wavelength divisionmultiplexer provided that one of the output ends is

closed.(ii) A star couplers or multi port coupler : A starcoupler is used to distribute an optical signal from asingle input fiber to multiple output fibers. Here manyfibers are bundled, twisted, heated and pulled at thetwisted area to get fiber fused biconical taper starcoupler.

Fiber connectors

Before connecting one fiber with the other fiber in thefiber optic communication link, one must decidewhether the joint should be permanent or demountable.Based on this, we have two types of joints. Apermanent joint is done bysplice and a demountable joint is done byconnector . Requirements of a good connector

1. At connector joint, it should offer low couplinglosses.

2. Connectors of the same type must be compatiblefrom one manufacturer to another.

3. In the fiber link, the connector design should besimple so that it can be easily installed.


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4. Connector joint should not be affected bytemperature, dust and moisture. That is, it shouldhave low environmental sensitivity.

5. It should be available at a lower cost and have aprecision suitable to the application.

Figure 8 shows the expanded beam connectoremploying collimating lens at the end ofthe transmitting fiber and focusing lens at the entranceend of the receiving fiber. The collimating lensconverts the light from the fiber into a parallel beam oflight and the focusinglens converts the parallel beam of light into a focusedbeam of light on to the core of thereceiving fiber.The lenses are antireflection coatedspherical micro lenses. To avoid losses due to fresnelreflection at the fiber-fiber joint, it is better to use anindexmatching fluid in the gap between the jointedfibers. When the index matching fluid has the same

refractive index as the fiber core, Fresnel reflectionlosses are completely eliminated. But if there is anyangular misalignment between fibers, there is anincreased loss for the fibers with index matching fluidthan for the fibers with air gap.

Figure 7. Connectors using butt-joint alignmentdesigns.

Figure 8. Expanded beam connector.

CONCLUSION

At present there are many optical fiber communicationlinks throughout the world without using opticalsolitons. When we introduce optical solitons as lightpulses through the fibers, we can achieve high qualitytelecommunication at a lower cost. We can expect agreat revolution in optical fiber communication withina few years by means of solitons.

REFERENCES

[1] T Okoshi and K Kikuchi,Coherent optical fibercommunication

[2] A Hasegawa,Optical solitons in fibers (SpringerVerlag, New York, 1989)

[3] S E Millar and I P Kaminow, eds,Optical fibertelecommunications - II (Academic, New York,1988)

[4] G P Agrawal, Nonlinear fiber optics (Academic,New York, 1989)

[5] C Yeh, Handbook of fiber optics (Academic,New York, 1990)


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LOW POWER DESIGN TECHNIQUES FOREMBEDDED SYSTEMS: CIRCUIT LEVEL

Dillip Kumar Mishra Asso .Professor

NM Institute of Engineering & [email protected]

ABSTRACT High level synthesis has aroused considerable interest in the recent years. While a lot of effort has been put intosynthesis for speed and area, power optimization has been explored only recently. Estimation of power consumption ofa design is the first step towards integrating power minimization techniques into any synthesis system. Low powerVLSI design can be achieved at various design abstraction levels starting form the algorithmic (behavioral) andsystem levels, and ending to layout and circuit levels.

INTRODUCTION

It has been demonstrated by several researchers that thedesign decisions made at the highest levels(architecture, algorithm, and system) have a dramaticimpact on power reduction [2], [3]. These suggest that

high level power exploration and analysis is extremelyuseful. However, behavioural level power estimationhas not been addressed so far. Behavioural levelestimation is essential because lower level estimationtools are time consuming and their use precludes acomplete exploration of the design space. Furthermore,the information necessary to perform this type ofanalysis is generally not available at the specificationtime.

Recently, the concept of providing personalcommunication and computing services in a portableenvironment has stirred a great deal of interest in bothcommercial and research areas. An integral componentof the proposed personal communications system wouldbe a portable multi-media terminal. Unfortunately, aswith all portable, battery-operated applications, powerdissipation becomes a critical issue. Furthermore, thehigh-cost of packaging and cooling power-hungrydevices has led to increasing efforts aimed atminimizing power consumption even in highperformance, non-portable systems.

Most contemporary design techniques andtools, however, give only passing consideration topower minimization, concentrating instead on delay andarea optimisation. The increasing importance ofportable applications such as personal communications

system will, therefore, force designers to revaluateperformance criteria for this growing class of systems.Moreover, these new design objectives will propeldesigners to seek new methodologies specificallytargeted at low power VLSI systems.

Clearly, a low-power CAD framework isrequired to support this endeavour. Ideally, these toolsshould provide not only for the exploration of issuesrelated to low-power design, but also for the automatedsynthesis of low-power systems. Not surprisingly, thesuccess of this environment will depend critically onthe availability of fast and accurate estimation of thekey design space parameters: area, delay, and power.

The objective of this report is to give aoverview of the different approaches to theoptimization techniques for low power design, and alsoa introduction for power estimation and the field oftools for designing. The remainder of the report isorganized as follows. In the 1st section presents a brief


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definition of power estimation, while in the 2nd describes the different techniques for optimization.

1. POWER ESTIMATIONPower estimation refers to the process of determiningwith a high level of confidence, the power consumed bya circuit. Power estimation is the first step towardsimplementing power minimization in VLSI systems.The most general and the most accurate powerestimation may be performed at the circuit level usingtools such as SPICE. Although estimation at such a lowlevel is very accurate, the time taken for the estimationprecludes the use of this technique for large circuits.For large circuits, it is therefore essential to estimatepower at higher levels of abstraction in the designprocess [20]. Three parameters which are used tocompare different estimation methods are Efficiency,Accuracy and Available information. Efficiency of amethod determines the maximum size of the circuit forwhich the method can do the estimation in reasonabletime. Accuracy determines the maximum error thatmust be tolerated with respect to the true or baselinepower estimator. Available information has to do withthe fact that many times, estimation must be done evenin the absence of implementation details. Any powerestimation method must therefore make optimum use ofavailable information to provide the best accuracy in anefficient manner. At the logic level, a more simplifiedpower dissipation model is used, leading to a fasterpower estimation process. Although detailed circuitbehavior is not modeled, the estimation values can stillbe reasonably accurate. Obtaining fast power estimatesis critical in order to allow a designer to comparedifferent designs. Further, for the purpose of directing adesigner or a synthesis tool for low power design, ratherthan an absolute measure of how much power aparticular circuit consumes, an accurate relative powermeasure between two designs will suffice.

A good compromise between accuracy andcomplexity is switch-level simulation. Simulation ofentire chips can be done within reasonable amounts ofCPU time [18, 19]. This property makes switch-levelsimulation very important power diagnosis tools. Afterlayout and before fabrication these tools can be used toidentifyhot spots in the design, i.e., areas in the circuitwhere current densities or temperature may exceed thesafety limits during normal operation.

1.2 Power dissipation model

There are three major sources of power dissipation indigital CMOS circuits, which can be summarized in thefollowing equation [1], [4]:

DDleak DDSC DD V I N f V Q N f V C P ++=2

21

Where:P : Total Power

DDV : Supply power f : Frequency of operationC : Node capacitance N : switching activity.

The first term

DDleak V I represents the power dissipated owing to leakagecurrent, which is primarily determined by thefabrication technology and consists of the followingcomponents:

a) The current drawn in reverse biased pn junctions, which are formed between thesource and drain diffusion regions and the bulkregion in a MOSFET,

b) The subthreshold current which arises from theinversion charge that exists at gate voltagesbelow the threshold voltage.

The second term

N f V Q DDSC which is called short-circuit power dissipation, is drawnin a circuit when a direct dc path from supply voltage toground appears for a short time interval, especiallyduring switching of a node. This component of power isfound being dependent on transistor sizes, input andoutput signal slopes, and output load.Finally, the third term

N f V C DD 2

21

in the equation above represents the power dissipationof a circuit due to charging and discharging of the loadcapacitance at every node.C is the load capacitance ofa particular node, dd V is the supply voltage, N is theswitching activity of this node, saying its averagenumber of transitions per sample period, and fit is thesample frequency [1].

All optimization techniques described assume that theclock frequency f and power supply voltagedd V havebeen defined previously. Reducing the clock frequencyis an obvious way to reduce power dissipation.However, many designers are not willing to accept theassociated performance penalty. In fact, the figure ofmerit used by many designers is Mops/mW , million ofoperations permW , and this value stays constant for

different values of f .[10]Even better is to reduce the supply voltage, given thequadratic relationship with power. However, reducingthe supply voltage increases significantly the signalpropagation delays, decreasing the maximum operatingfrequency and thus again reducing the system'sperformance.


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Given optimal f and DDV , the problem of optimizing

a circuit for low power is to minimize:

iii N C : switched capacitance

Possibilities:

Reducing the global circuit capacitanceRedistributing the switching in the circuitIt has been proved that this component of power is thedominant source of power dissipated in digital circuits,and low-power design thus becomes the task ofminimizing N , C , dd V and f , while retaining therequired functionality. Several research efforts, at everyabstract level, have been made in order to limit downthese factors.In the following sections is described some verycommon techniques for low-power design at the gate-level optimization, in order to reduce the switchingactivity of a circuit. It is notable to say that the loadcapacitance minimization is achieved by layoutoptimization strategies, while the other two factors aremainly affected by high-level synthesis methods.

2. POWER DISSIPATION MODEL

2.1 Optimization at Circuit Level Several circuit-level techniques are available to thelow-power designer. These techniques include carefulselection of a circuit style: static vs. dynamic,synchronous vs. asynchronous, fully-complementaryvs. pass-transistor, etc. Other techniques involvetransistor sizing or selection of a design methodologysuch as full-custom or standard cell. Some of thesetechniques can be applied in conjunction with higherlevel power reduction techniques. When possible,designers should take advantage of this fact and exploitboth low and high-level techniques in concert. Often,however, circuit-level techniques will conflict with thelow-power strategies based on higher abstraction levels.In these cases, the designer must determine, whichtechniques offer the largest power reductions. Circuitlevel techniques typically offer reductions of a factor oftwo or less, while some higher level strategies withtheir more global impact can produce savings of anorder of magnitude or more. In such situations,considerations imposed by the higher-level techniqueshould dominate and the designer should employ thosecircuit-level methodologies most amenable to theselected highlevel strategy.

2.1.1 Transistor Sizing Regardless of the circuit style employed, the issue oftransistor sizing for low power arises. The primarytrade-off involved is between performance and cost -where cost is measured by area and power. Transistors

with larger gate widths provide more current drive thansmaller transistors. Unfortunately, they also contribute more devicecapacitance to the circuit and, consequently, result inhigher power dissipation. Moreover, larger devicesexperience more severe short-circuit currents, whichshould be avoided whenever possible. In addition, if alldevices in a circuit are sized up, then the loadingcapacitance increases in the same proportion as thecurrent drive, resulting in little performanceimprovement beyond the point of overcoming fixedparasitic capacitance components. In this sense, largetransistors becomeself-loading and the benefit of largedevices must be reevaluated. A sensible low-powerstrategy is to use minimum size devices wheneverpossible. Along the critical path, however, devicesshould be sized up to overcome parasitics and meetperformance requirements. [22,23]Transistor sizing for minimum area is a well established

problem [25]. There is a subtle difference between thisproblem and sizing for low power. If the critical delayof the circuit exceeds the design specifications and thussome transistors need to be resized, methods forminimum area will focus on minimizing the totalenlargement of the transistors. On the other hand,methods for low power will first resize those transistorsdriven by signals with lower switching activity.Transistor sizing in a combinationalgate circuit can

have significant impact on circuit delay and powerdissipation. If the transistors in a given gate areincreased in size, then the delay of the gate decreases,however, power dissipated in the gate increases.Further, the delay of the fanin gates increases becauseof increased load capacitance. Given a delay constraint,finding an appropriate sizing of transistors thatminimizes power dissipation is a computationallydifficult problem. A typical approach to the problem isto compute the slack at each gate in the circuit, wherethe slack of a gate corresponds to how much the gatecan be slowed down without affecting the critical delayof the circuit. Subcircuits with slacks greater than zeroare processed, and the sizes of the transistors reduceduntil the slack becomes zero, or the transistors are allminimum size .

2.2 Optimization at Logic Level This section discuss several gate-level techniques forpower optimization. The main concepts explored werereducing the waste associated with unnecessary activityand trading power for performance through low-voltageconcurrent processing. The gains reported by low-power designers working at the gate level are typicallyon the order of a factor of two or less.

2.2.1 Path Balancing

The way the gates of a logic circuit areinterconnected can strongly affect the overall switching


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activity, and hence the power dissipatiotiming skew between signals in a cispurious transitions (glitches) resulting[10]. To reduce the possible spurioucircuit, delay of all true paths that convemust be balanced.

Path balancing can be actechnology mapping by selective colladecomposition or after technology mainsertion and pin reordering. The adtechnique is that by selectively collapsia node, the arrival time at the outpdifference between the inputs of thedriving high capacitive nodes. Ainserting variable-delay buffers in a circall paths in the circuit can be made equdelay insertion is to use the minimum nelements (o achieve the maximumglitching activity). Path delays maybalanced by an appropriate signal to theThis is possible, because the delay cCMOS gates vary as a function of the Icausing a transition at the output. This aincrease the critical delay of the circuit,tively eliminate spurious transitions.addition of buffers increases capacitaoffset the reduction in switching activity

Fig. 1 Path Balancing

2.2.2 Dont-care Optimization Any gate in a combinational circuit hacontrollability and observability doncontrollability dont-care set corresponcombinations that never occur at the gobservability dont-care set correspondof input combinations that produce thethe circuit outputs. The power dissipatdependent on the probability of the gate1 or a 0. This probability can be chanthe dont-care sets [16].

n. For example,cuit can causein extra power

s activity in arge at each gate

hieved beforepsing and logicpping by delayantage of thisg the fanins oft of the nodenodes that areditionally, by

uit the delays ofal. The issue inumber of delay

reduction insometimes be

pin assignment.aracteristics ofnput pin that isddition will notand will effec-

However, thece which may.

s an associated-care set. Theds to the inputate inputs. Thes to collectionssame values aton of a gate isevaluating to aed by utilizing

Traditionally don't-care sarea minimization. Recently teproposed for the use of don't-switching activity at the output of

The structure of the logsome combinations over nodes A,These combinations form theSatisfiability Dont-Care Set (Sthere may be some input combinvalue ofF is not used in the compof the circuit. The set of these ctheObservability Dont-Care Set(

Fig. 2 Satisfiability or Observab

2.2.3 Technology Mapping

Once optimized logicobtained, the task remains to maptarget library that contains optimichosen technology. A typicalhundreds of gates with differModern technology mapping m

covering formulation, to targetfunctions.The graph covering fo

extended to the power cost funcdelay model, the optimal mappidetermined in polynomial time [12As long as the delay constraints areusually willing to make some tradpower dissipation

The graph covering forbeen extended to use witched capcost function. The main strategydissipation is to hide nodes with hwithin complex logic elements asto gates are generally much smalle

Technology decompositioto the process of transformingdescription of a logic network intoa given gate-level network herecircuit-level implementations. Finput NAND can be implementedCMOS gate or as a cascade of si

Dillip Kumar Mishra

ts have been used forhniques have been

cares to reduce thea logic gate.ic circuit may imply B and C never occur.

Controllability orC) of F. Similarly,ations for which theutation of the outputsmbinations is calledDC).

ility Dont-Care Set

quations have beenthe equations into aed logic-gates in the

library will containnt transistor sizes.

ethods use a graph

area and delay cost

rmulation has beention. Under the zerong of a tree can be].till met, the designer isoff between area and

ulation of [12] hasacitance as part of the

to minimize powerigh switching activitycapacitances internalr.n and mapping refersa gate-level booleana CMOS circuit. Foray be many possibler instance, a three-

as a single complexpler two-input gates.


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Each mapping may result in different signal activities,as well as physical capacitances. For example, complexgates tend to exhibit an overall lower physicalcapacitance since more signals are confined to internalnodes rather than to the more heavily loaded outputnodes. The concept of technology mapping for low-

power is to first decompose the boolean network suchthat switching activity is minimized, and then to hideany high activity nodes inside complex CMOS gates. Inthis way, rapidly switching signals are mapped to thelow capacitance internal nodes, thereby reducing powerconsumption. Making a gate too complex, however, canslow the circuit, resulting in a trade-off of performancefor power. Several technology mapping algorithms forlow power have been developed and offer an averagepower reduction of 12% down to 21% [26, 27].

Fig. 3 Difference Between Technology and PowerArea Mapping [27]

Consider the circuit in Figure 3(a). The signal transitionprobabilities at the outputs of gates G1, G2 and G3 are0.109 0.109 and 0.179, respectively. Assume that thegates available in the library for technology mappingare inverters, two-input and three-input NAND gatesand AOI33 gates. The areas and capacitances in standardunits associated with these gates are shown in Figure3(b). The minimum, area mapping for this circuit isshown in Figure 3(c) and minimum-power mapping inFigure 3(d). The area and power cost of each mappingis shown in the corresponding figure. The power cost ofa mapping is the sum of the power costs of each matchin the mapping. Using the power models, the totalpower cost of the minimum-area mapping is 0.0907while that for the minimum power mapping is 0.0803.Note that since the signal transition probability at the

output of gate G3 is much higher than the signaltransition probabilities at the outputs of gates G1 andG2, it is less expensive in terms of power dissipation tohave large gates feeding the outputs of gates G1 and G2 and small gates feeding the output of gate G3, than havelarge gates feed the output of gate G3. It turns out that

the minimum-area mapping has a large gate and aninverter feeding the wires with high signal transitionprobability, and is therefore expensive in terms ofpower dissipation. As we can see from the figure, thepower cost of the minimum-power mapping is found tobe more than 10% lower than the power cost of theminimum-area mapping.

The similarity between technology mappingfor power and delay is that the cost of a match is, inpart, dependent on the load driven by the match. In themost general case of the use of a non-zero-delay modelin the computation of signal transition probabilities, thebest match at a node cannot be determined until thematches at the fanout nodes and the matches at theirtransitive fanins have been chosen. In the specializedcase of the zero-delay model, the signal transitionprobability at the output of a node is independent of thematch chosen for that node. Therefore, the powerdissipated in the load capacitance is the same for allmatches at the node. Consequently, the best match at anode can be determined before the matches at thefanout nodes have been chosenas in the case of technology mapping for area. Even sothe actual cost of the best match at a node can only bedetermined once the matches at the fanout nodes areknown.

2.2.4 Retiming

Retiming is a well-known optimization methodthat repositions the flip-flops in a synchronoussequential circuit so as to minimize the required clockperiod. Polynomial-time algorithms for minimum delayretiming and minimum-register retiming have beendeveloped. It has been observed that the switchingactivity at flip-flop outputs in a synchronous sequentialcircuit can be significantly less than the activity at theflip-flop inputs. This is because there may be manyspurious transitions at the inputs to the flip-flops whichare filtered out by the clock [14, 15].

Consider the circuit of Figure 4 f the averageswitching activity at the output of gateg is N g and theload capacitance isC L, then the power dissipated at theoutput of this gate is proportional to

N g C L

Now consider the situation when a flip-flop R is addedto the output ofg, as illustrated in Figure 4. The powerdissipated by the circuit is now proportional to

N g C R + N R C L


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where N g is as before,C R is the capacitinput to the flip-flop, and N R is the avactivity at the flip-flop output. The mhere is that

N R < N g

since the flip-flop output will maktransition at the beginning of the clexample, the gateg may glitch atransitions as shown in the figure, boutput will make at most one transitionis asserted. This implies that is possible

N g C R + N R C L < N g C L if both N g and C L are high. Thus, theflops to a circuit may actually ddissipation. Since adding flip-flops tocommon way to improve the performaby pipelining it, it is worthwhile toramifications of this observation. [7, 8]

Fig. 4 Adding a Flip-Flop to a Circuit

Fig. 6 Moving a

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