This document summarizes different waveform coding techniques used for analog to digital conversion in communications systems. It describes the basic principles and processes of Pulse Code Modulation (PCM), Differential Pulse Code Modulation (DPCM), Delta Modulation (DM), and Adaptive Delta Modulation (ADM). Key steps like sampling, quantization, encoding, and decoding are discussed for each technique. The techniques are then compared in terms of their advantages, disadvantages, and applications in signal transmission.
Hello everyone. This is a short presentation on path loss and shadowing. I have not covered all the topics but a brief idea is given on path loss and wireless channel propagation models.
Hope you find it useful.
Thanks
Base band transmission
*Wave form representation of binary digits
*PCM, DPCM, DM, ADM systems
*Detection of signals in Gaussian noise
*Matched filter - Application of matched filter
*Error probability performance of binary signaling
*Multilevel base band transmission
*Inter symbol interference
*Eye pattern
*Companding
*A law and μ law
*Correlation receiver
Hello everyone. This is a short presentation on path loss and shadowing. I have not covered all the topics but a brief idea is given on path loss and wireless channel propagation models.
Hope you find it useful.
Thanks
Base band transmission
*Wave form representation of binary digits
*PCM, DPCM, DM, ADM systems
*Detection of signals in Gaussian noise
*Matched filter - Application of matched filter
*Error probability performance of binary signaling
*Multilevel base band transmission
*Inter symbol interference
*Eye pattern
*Companding
*A law and μ law
*Correlation receiver
The attached narrated power point presentation attempts to explain the methods of computation of total power loss and system rise time in a fiber optic link. The material will be useful for KTU final year B Tech students who prepare for the subject EC 405, Optical Communications.
Frequency-Shift Keying, also known as FSK is a type of digital frequency modulation. It is also often called as binary frequency shift keying or BFSK
Similar to analog FM, it is a constant-amplitude angle modulation.
This presentation will discuss the concepts behind FSK
The attached narrated power point presentation offers a block level and an elementary level mathematical treatment of optical communication systems employing coherent detection. The material will immensely benefit KTU final year B Tech students who prepare for the subject EC 405, Optical Communications.
The typical three path propagation and anti jamming capability associated with DSSS were carried out
through the combination of Lab VIEW and MATLAB 7.8. At the transmitter, the NRZ data stream is first mapped
into BPSK symbols and then spread-out using different PN code like Hadamard code, Gold or Kasami sequences.
And we see that single user is not total utilization band. Direct Sequence Spread Spectrum (DSSS) techniques are
used same bandwidth Number of user to increase, and we see that better performance. That we can say Direct
Sequence Spread Spectrum techniques is reused to bandwidth. And we can say that in this techniques power loss is
low, anti jamming capability is less and system is more reliable. Furthermore, BPSK-Spreading transceiver should be
analyzed for their performance, multipath scenario and interference whether under AWGN channel which show that
these has been overcome effectively and attain more robust performance, when using direct sequence spread
spectrum.
PAPR REDUCTION OF OFDM SIGNAL BY USING COMBINED HADAMARD AND MODIFIED MEU-LAW...IJCNCJournal
Orthogonal frequency division multiplexing (OFDM) is a technique which gives high quality of service (QOS) to the users by mitigating the fading signals as well as high data rates in multimedia services. However, the peak-to-average power ratio (PAPR) is a technical challenge that reduces the efficiency of RF power amplifiers. In this paper, we propose the combined Hadamard transform and modified meu-law companding transform method in order to lessen the effects of the peak-to-average power ratio of the
OFDM signal. Simulation results show that the proposed scheme reduces PAPR compared to other companding techniques as well as the Hadamard transform technique when used on its own.
The attached narrated power point presentation attempts to explain the methods of computation of total power loss and system rise time in a fiber optic link. The material will be useful for KTU final year B Tech students who prepare for the subject EC 405, Optical Communications.
Frequency-Shift Keying, also known as FSK is a type of digital frequency modulation. It is also often called as binary frequency shift keying or BFSK
Similar to analog FM, it is a constant-amplitude angle modulation.
This presentation will discuss the concepts behind FSK
The attached narrated power point presentation offers a block level and an elementary level mathematical treatment of optical communication systems employing coherent detection. The material will immensely benefit KTU final year B Tech students who prepare for the subject EC 405, Optical Communications.
The typical three path propagation and anti jamming capability associated with DSSS were carried out
through the combination of Lab VIEW and MATLAB 7.8. At the transmitter, the NRZ data stream is first mapped
into BPSK symbols and then spread-out using different PN code like Hadamard code, Gold or Kasami sequences.
And we see that single user is not total utilization band. Direct Sequence Spread Spectrum (DSSS) techniques are
used same bandwidth Number of user to increase, and we see that better performance. That we can say Direct
Sequence Spread Spectrum techniques is reused to bandwidth. And we can say that in this techniques power loss is
low, anti jamming capability is less and system is more reliable. Furthermore, BPSK-Spreading transceiver should be
analyzed for their performance, multipath scenario and interference whether under AWGN channel which show that
these has been overcome effectively and attain more robust performance, when using direct sequence spread
spectrum.
PAPR REDUCTION OF OFDM SIGNAL BY USING COMBINED HADAMARD AND MODIFIED MEU-LAW...IJCNCJournal
Orthogonal frequency division multiplexing (OFDM) is a technique which gives high quality of service (QOS) to the users by mitigating the fading signals as well as high data rates in multimedia services. However, the peak-to-average power ratio (PAPR) is a technical challenge that reduces the efficiency of RF power amplifiers. In this paper, we propose the combined Hadamard transform and modified meu-law companding transform method in order to lessen the effects of the peak-to-average power ratio of the
OFDM signal. Simulation results show that the proposed scheme reduces PAPR compared to other companding techniques as well as the Hadamard transform technique when used on its own.
FPGA Design & Simulation Modeling of Baseband Data Transmission SystemIOSR Journals
Abstract: This paper describes a study on a baseband data transmission system developed for undergraduate
students studying communication engineering. Theoretical material, developed in the lectures, is briefly
covered. A practical system is presented with pre-detection filtering being employed to improve the bit error
rate. A simulation of the complete system is carried out on a Sun work station using the MATLAB simulation
package. Simulation and theoretical results are compared.
Performance Analysis of PAPR Reduction in MIMO-OFDMIJARBEST JOURNAL
Authors: Jayaraman.G1, VeeraKumar K2, Selvakani.S3
Abstract— In communication system, it is aimed to provide highest possible
transmission rate at the lowest possible power and with the least possible noise. MIMOOFDM
has been chosen for high data rate communications and widely deployed in many
wireless communication standards. The major drawback in OFDM signal transmission is
high PAPR. In previous, use clipping technique to tackle this problem. In this paper, use
EM-GAMP algorithm to reduce PAPR in considerable amount.
Performance analysis of papr reduction techniques in multicarrier modulation ...eSAT Publishing House
IJRET : International Journal of Research in Engineering and Technology is an international peer reviewed, online journal published by eSAT Publishing House for the enhancement of research in various disciplines of Engineering and Technology. The aim and scope of the journal is to provide an academic medium and an important reference for the advancement and dissemination of research results that support high-level learning, teaching and research in the fields of Engineering and Technology. We bring together Scientists, Academician, Field Engineers, Scholars and Students of related fields of Engineering and Technology.
Compressive spectrum sensing using two-stage scheme for cognitive radio netwo...IJECEIAES
The modern applications of communications that use wideband signals suffer the lacking since the resources of this kind of signals are limited especially for fifth generation (5G). The compressive spectrum sensing (COMPSS) techniques address such issues to reuse the detected signals in the networks and applications of 5G. However, the raw techniques of COMPSS have low compression ratio and high computational complexity rather than high level of noise variance. In this paper, a hybrid COMPSS scheme has been developed for both non-cooperative and cooperative cognitive radio networks. The proposed scheme compiles on discrete wavelet transform single resolution (DWT-SR) cascaded with discrete cosine transform (DCT). The first is constructed according to the pyramid algorithm to achieve 50% while the second performed 30% compression ratios. The simulation and analytic results reveal the significant detection performance of the proposed technique is better than that of the raw COMPSS techniques.
Performance analysis of papr reduction techniques in multicarrier modulation ...eSAT Journals
Abstract Orthogonal FrequencyDivisionMultiplexing (OFDM) is one of the many multicarrier modulation techniques which provide high spectral efficiency, less vulnerability to echoes,low implementation complexity and resilience to non – linear distortion. It is used in communication systems due to its various advantages. However, while this system is implemented problem of high peak – to – average power ratio(PAPR) is encountered. The reason behind this drawback is the existence of manyindependent subcarriers, due towhichthesignal amplitudecanhavehighpeakvalues as compared to average of whole system. The high PAPR in multicarrier transmission systems causes power degradation and spectrum spreading.Interleaving, Tone Reservation, Peak Reduction Carrier,Block Coding, Active Constellation Extension, Envelope ScalingareamongmanyPAPRreductionschemesthathavebeenproposedas a remedy to thisproblem. In this paper, performances of Amplitude Clipping and Filtering, Selected Level Mapping (SLM), and PartialTransmitSequence (PTS) techniques of PAPR reduction in OFDM systems by parameter variations are analyzed, based on Complementary Cumulative Distribution Function. An attempt has been made to simulate clipping and filtering technique with iterations and the simulation shows that PAPR problem is reduced as number of iterations increases. The attempts have also been made to simulate SLM technique and PTS technique by varying number of phase sequences, number of sub-blocks in SLM, PTS respectively and simulation results shows that by increasing the number of phase sequences, sub-blocks, PAPR can be reduced significantly.The mathematical equations are incorporated here to compute the maximum expected PAPR from an OFDM signal which shows when there is phase alignment of all sub carriers and sub carriers are equally modulated, then signal peak value hits the maximum. Besides these computer simulations, a comparative study of these three techniques is done.
Capacity Enhancement of MIMO-OFDM System in Rayleigh Fading ChannelIOSR Journals
MIMO-OFDM system in Rayleigh Fading Channel is very popular technique for mobile
communication now a day’s for research. Here we want increase the capacity of MIMO-OFDM of system by
using adaptive modulation, Algebraic Space-Time Codes (ASTC) encoder for MIMO Systems are based on
quaternion algebras .we found that ergodic capacity has some limitation which reduce the system’s
performance to overcome this we use ASTC code . ASTC code are full rank, full rate and non vanishing constant
minimum determinant for increasing spectral efficiency and reducing Peak to Average Power Ratio (PAPR) .
Capacity Enhancement of MIMO-OFDM System in Rayleigh Fading ChannelIOSR Journals
Abstract: MIMO-OFDM system in Rayleigh Fading Channel is very popular technique for mobile communication now a day’s for research. Here we want increase the capacity of MIMO-OFDM of system by using adaptive modulation, Algebraic Space-Time Codes (ASTC) encoder for MIMO Systems are based on quaternion algebras .we found that ergodic capacity has some limitation which reduce the system’s performance to overcome this we use ASTC code . ASTC code are full rank, full rate and non vanishing constant minimum determinant for increasing spectral efficiency and reducing Peak to Average Power Ratio (PAPR) . Keywords— Adaptive modulation ASTC code, Capacity, BER, Ergodic capacity, PAPR, Spectral Efficiency and SNR
Analyses and performance of techniques papr reduction for stbc mimo ofdm syst...ijwmn
An OFDM system is combined with multiple-input mult
iple-output (MIMO) in order to increase the
diversity gain and system capacity over the time va
riant frequency-selective channels. However, a maj
or
drawback of MIMO-OFDM system is that the transmitte
d signals on different antennas might exhibit high
peak-to-average power ratio (PAPR).In this paper, w
e present a PAPR analysis reduction of space-time-
block-coded (STBC) MIMO-OFDM system for 4G wireless
networks. Several techniques have been used to
reduce the PAPR of the (STBC) MIMOOFDM system: clip
ping and filtering, partial transmit sequence
(PTS) and selected mapping (SLM). Simulation result
s show that clipping and filtering provides a bette
r
PAPR reduction than the others methods and only SLM
technique conserve the PAPR reduction in
reception part of signal.
Improving the error performance of offset pulse position modulation using Re...IJECEIAES
An innovative performance study of an offset pulse-position modulation (OPPM) scheme is presented in this work with Reed–Solomon (RS) and low-density parity-checking (LDPC). The main aim is to resolve the errors of OPPM three using an RS or LDPC as a sporadic set of forward error correction (FEC). In this regard, the separate FEC has been utilized with coding that is based on multi-level, and waveform shaping based on the trellis. To systematically conduct this research, the greatest transmission efficiency that associated with the optimum RS code rates at different fiber normalization bandwidths is evaluated. Furthermore, the transmission efficiencies, channel extension, as well as the required number of photons per pulse of OPPM before and after the integration with RS or LDPC are compared. The results indicate an enhancement of mitigating the system's bit error rate and delivering more error-free data to the receiver in the occasion of applying the optimal settings of the RS or LDPC.
Tractable computation in outage performance analysis of relay selection NOMATELKOMNIKA JOURNAL
In recent years, using full-duplex (FD) transmission model provides enhanced bandwidth efficiency and improved performance for non-orthogonal multiple access (NOMA) system. However, lack of papers have investigated FD relay together with relay selection issue to improve performance of NOMA system. The problems in power allocation for two NOMA users satisfying fairness as well as relay selection strategy are studied in this paper. By considering the outage performance of proposed scheme with its vital result, general NOMA wireless networks can be developed for future networks due to its improved performance. Simulation results show that the relaying selection scheme can achieve a significant performance improvement by increasing required quantity of relay.
CS Based Channel Estimation for OFDM Systems under Long Delay Channels Using ...IJERA Editor
Orthogonal frequency division multiplexing (OFDM) is a technique which are used in the next-generation wireless communication. Channel estimation in the OFDM technique is one of the big challenges, ever since high-resolution channel estimation can significantly improve the equalization at the receiver and consequently enhance the communication performances. Channel computation using superimposed pilot sequences is also a fully new area, idea for using superimposed pilot sequences has been proposed by various authors for different applications. In this paper, we are introduced a high accurate, low complexity compressive sensing (CS) based channel estimation namely Auxiliary information based Subspace Pursuit (ASP) in TFT-OFDM systems. ASP based channel estimation in TFT-OFDM system is based on two steps. First is, by exploiting the signal structure of recently proposed TDM-OFDM scheme, the supporting channel information is obtained. Second is, we propose the supporting information based subspace pursuit (SP) algorithm to use a very small amount of frequency domain pilots embedded in the OFDM block used for the exact channel estimation. Moreover, the obtained auxiliary channel information is adopted to reduce the complexity of the conventional SP algorithm. Simulation results demonstrate a important reduction of the number of pilots relative to least-squares channel estimation and supporting high-order modulations like 256 QAM.
Reduction of PAPR and Efficient detection ordering scheme for MIMO Transmissi...IJERA Editor
The technical challenges for communication engineers is the development of best performance wireless
networks with negligible amount of distortions. We have to consider multipath propagation attenuation and
radio spectrum inefficiency. Now a days, In MIMO (Multi Input Multi Output) systems there is a huge demand
for the networks with the high transmission rates and better quality of service which are having low PAPR ratio.
Instead of OFDMA, filter banks are used in massive MIMO to reduce the complexity. But they are error prone
to noise. This base paper discusses about PAPR reduction in MIMO systems using different precoding based
OFDM systems. Mainly, minimization of multi-antenna systems by controlling the transmission power and
reduction of PAPR using ZC (Zadoff-Chu) matrix transform.
BER Performance of MU-MIMO System using Dirty Paper CodingIJEEE
In this paper Dirty Paper Coding for communication system is implemented. MIMO application that involves devices such as cell phones, pocket PCs require closely spaced antenna, which suffers from mutual coupling among antennas and high spatial correlation for signals. DPC is used for compensating the degradation due to correlation and mutual coupling.
Synthetic Fiber Construction in lab .pptxPavel ( NSTU)
Synthetic fiber production is a fascinating and complex field that blends chemistry, engineering, and environmental science. By understanding these aspects, students can gain a comprehensive view of synthetic fiber production, its impact on society and the environment, and the potential for future innovations. Synthetic fibers play a crucial role in modern society, impacting various aspects of daily life, industry, and the environment. ynthetic fibers are integral to modern life, offering a range of benefits from cost-effectiveness and versatility to innovative applications and performance characteristics. While they pose environmental challenges, ongoing research and development aim to create more sustainable and eco-friendly alternatives. Understanding the importance of synthetic fibers helps in appreciating their role in the economy, industry, and daily life, while also emphasizing the need for sustainable practices and innovation.
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Biological screening of herbal drugs: Introduction and Need for
Phyto-Pharmacological Screening, New Strategies for evaluating
Natural Products, In vitro evaluation techniques for Antioxidants, Antimicrobial and Anticancer drugs. In vivo evaluation techniques
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June 3, 2024 Anti-Semitism Letter Sent to MIT President Kornbluth and MIT Cor...Levi Shapiro
Letter from the Congress of the United States regarding Anti-Semitism sent June 3rd to MIT President Sally Kornbluth, MIT Corp Chair, Mark Gorenberg
Dear Dr. Kornbluth and Mr. Gorenberg,
The US House of Representatives is deeply concerned by ongoing and pervasive acts of antisemitic
harassment and intimidation at the Massachusetts Institute of Technology (MIT). Failing to act decisively to ensure a safe learning environment for all students would be a grave dereliction of your responsibilities as President of MIT and Chair of the MIT Corporation.
This Congress will not stand idly by and allow an environment hostile to Jewish students to persist. The House believes that your institution is in violation of Title VI of the Civil Rights Act, and the inability or
unwillingness to rectify this violation through action requires accountability.
Postsecondary education is a unique opportunity for students to learn and have their ideas and beliefs challenged. However, universities receiving hundreds of millions of federal funds annually have denied
students that opportunity and have been hijacked to become venues for the promotion of terrorism, antisemitic harassment and intimidation, unlawful encampments, and in some cases, assaults and riots.
The House of Representatives will not countenance the use of federal funds to indoctrinate students into hateful, antisemitic, anti-American supporters of terrorism. Investigations into campus antisemitism by the Committee on Education and the Workforce and the Committee on Ways and Means have been expanded into a Congress-wide probe across all relevant jurisdictions to address this national crisis. The undersigned Committees will conduct oversight into the use of federal funds at MIT and its learning environment under authorities granted to each Committee.
• The Committee on Education and the Workforce has been investigating your institution since December 7, 2023. The Committee has broad jurisdiction over postsecondary education, including its compliance with Title VI of the Civil Rights Act, campus safety concerns over disruptions to the learning environment, and the awarding of federal student aid under the Higher Education Act.
• The Committee on Oversight and Accountability is investigating the sources of funding and other support flowing to groups espousing pro-Hamas propaganda and engaged in antisemitic harassment and intimidation of students. The Committee on Oversight and Accountability is the principal oversight committee of the US House of Representatives and has broad authority to investigate “any matter” at “any time” under House Rule X.
• The Committee on Ways and Means has been investigating several universities since November 15, 2023, when the Committee held a hearing entitled From Ivory Towers to Dark Corners: Investigating the Nexus Between Antisemitism, Tax-Exempt Universities, and Terror Financing. The Committee followed the hearing with letters to those institutions on January 10, 202
Read| The latest issue of The Challenger is here! We are thrilled to announce that our school paper has qualified for the NATIONAL SCHOOLS PRESS CONFERENCE (NSPC) 2024. Thank you for your unwavering support and trust. Dive into the stories that made us stand out!
2024.06.01 Introducing a competency framework for languag learning materials ...Sandy Millin
http://sandymillin.wordpress.com/iateflwebinar2024
Published classroom materials form the basis of syllabuses, drive teacher professional development, and have a potentially huge influence on learners, teachers and education systems. All teachers also create their own materials, whether a few sentences on a blackboard, a highly-structured fully-realised online course, or anything in between. Despite this, the knowledge and skills needed to create effective language learning materials are rarely part of teacher training, and are mostly learnt by trial and error.
Knowledge and skills frameworks, generally called competency frameworks, for ELT teachers, trainers and managers have existed for a few years now. However, until I created one for my MA dissertation, there wasn’t one drawing together what we need to know and do to be able to effectively produce language learning materials.
This webinar will introduce you to my framework, highlighting the key competencies I identified from my research. It will also show how anybody involved in language teaching (any language, not just English!), teacher training, managing schools or developing language learning materials can benefit from using the framework.
Model Attribute Check Company Auto PropertyCeline George
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1. TERM PAPER ON
WAVEFORM CODING
Department of Electronics and Communication Engineering
Assessable Activity Based Learning (AAL)
By:
ALAPAN RANJAN BANERJEE
ROLL NO :- 03
YEAR :- 3RD
YEAR
REGISTRATION NO. :- 161220110132 OF 2016-2017
ST. THOMAS’ COLLEGE OF ENGINEERING AND TECHNOLOGY
Affiliated to
MAULANA ABUL KALAM AZAD UNIVERSITY OF TECHNOLOGY ,WEST BENGAL
2. INTRODUCTION
Althoughhumansare well equippedforanalogcommunications,analogtransmissionisnotparticularly
efficient.Whenanalogsignalsbecome weakbecause of transmissionloss,itishardto separate the
complex analogstructure fromthe structure of randomtransmissionnoise.If youamplifyanalogsignals,
it alsoamplifiesnoise,andeventuallyanalogconnectionsbecometoonoisytouse.Digital signals,
havingonly"one−bit"and"zero−bit"states,are more easilyseparatedfromnoise.Theycanbe
amplifiedwithoutcorruption.Digital codingismore immune tonoise corruptiononlong−distance
connections.Also,the world'scommunicationsystemshave convertedtoadigital transmissionformat
calledpulse code modulation(PCM).PCMisa type of codingthat is called"waveform"codingbecause it
createsa codedform of the original voice waveform.Thisdocumentdescribesata highlevel the
conversionprocessof analogvoice signalstodigital signals.
ANALOG TO DIGITAL CONVERSION
Sampling:take samplesattime nT
– T: samplingperiod;
– fs= 1/T: samplingfrequency
Quantization:mapamplitudevaluesintoasetof discrete valueskQ
– Q: quantizationinterval orstep size
BinaryEncoding
– Converteachquantizedvalue intoabinarycodeword
3. QUANTIZATION
A Q-levelquantizercomparesthe discrete-timeinputx(nT)withitsfixeddigital levels.Itassignsanyone
of the digital level tox(nT) withitsfixeddigital levels.Itthenassignsanyone of the digital level tox(nT)
whichresultsinminimumdistortionorerror.Thisiscalledquantizationerror.Thusthe otputof a
quantizerisa digital level.
Uniformquantization :-
o the quantizationlevelsare uniformlyspaced
o Applicable whenthe signal isinafinite range (fmin,fmax)
o The entire datarange is dividedintoLequal intervalsof length Q(knownas
quantizationinterval orquantizationstep-size) Q=(fmax-fmin)/L
o Interval i is mappedtothe middle value of thisinterval
o We store/sendonlythe index of quantizedvalue
o There are twotypesof uniformquantization.Theyare Mid-Rise type andMid-Tread
type.
Non-uniformquantization:-
If the quantizercharacteristicsisnonlinearandstepsize isnotconstantinsteadif it is
variable,dependedonthe amplitudeof inputsignal thenthe quantizationisknownas
nonuniformquantization.
The non-uniformquantizationispracticallyachievedbythe processcalled
COMPANDING.
COMPANDING:-
o The processof compressionof the signal atthe transmitterandexpansionatthe receiveris
calledascompanding(compressionandexpansion).
4. o In companding,the higheramplitudeanalogsignalsare compressedprecedingtransmission
and thenexpandedinthe receiver.
o Compandingisperformedwiththe helpof three functional blocks,whichare Compressor,
UniformquantizerandExpanderandthe diagramin shownbelow
o The compressorwill compressthe dynamicrange of the signal sothat highdynamicrange
signal can be passedthroughcomponentsof low dynamicrange capability,the uniform
quantizerwill undergothe quantizationprocessof the compressedsignal andthe lastlythe
expanderwillundergo expansionandinvertthe compressionfunctiontoreconstructthe
original signal.
o The expanderhascomplementarycharacteristicsasthatof compressorso that the
compressorinputisequal toexpanderoutputinordertoreproduce the signal atthe
receiver.
o belowillustratesthe input-outputcharacteristicsandcurvesof the compandingprocess,
and itcan be seenthatcompandinghaslinearcharacteristics.
Ideally,we needalinearcompressioncharacteristicsforsmall amplitudesof the inputsignal anda
logarithmiccharacteristicselsewhere.Inpractice,thisisdone byusingfollowingtwomethods:
1. A−law Companding
2. u−law Companding
5. A−lawCompander
Limitingthe linearsamplevaluestotwelve magnitude bits,the A−law compressionis
definedbythisequation,whereA isthe compressionparameter(A=87.7in Europe),and
x isthe normalizedintegertobe compressed.
u−lawCompander
Limitingthe linearsamplevaluestothirteenmagnitude bits,the u−law (u−law andMu−
laware usedinterchangeablyinthisdocument)compressionisdefinedbythisequation,
where mis the compressionparameter(m=255 in the U.S. and Japan) andx isthe
normalizedintegertobe compressed.
A−lawstandardis primarilyusedbyEurope andthe restof the world.u−law isusedby NorthAmerica
and Japan
PULSE CODE MODULATION (PCM)
In Pulse Code Modulation,the message signal isrepresentedbyasequence of codedpulses.This
message signal isachievedbyrepresentingthe signal indiscrete form inbothtime andamplitude.
6. Basic Elementsof PCMcommunication :-
o PCMtransmitter :-
Low PassFilter
Thisfiltereliminatesthe highfrequencycomponentspresentinthe inputanalog
signal whichisgreaterthanthe highestfrequencyof the message signal,to
avoidaliasingof the message signal.
Sampler
Thisis the technique whichhelpstocollectthe sample dataatinstantaneous
valuesof message signal,soasto reconstructthe original signal.The sampling
rate mustbe greaterthan twice the highestfrequencycomponent of the
message signal,inaccordance withthe samplingtheorem.
Quantizer
Quantizingisaprocessof reducingthe excessive bitsandconfiningthe data.
The sampledoutputwhengiventoQuantizer,reducesthe redundantbitsand
compressesthe value.
Encoder
The digitization of analog signal is done by the encoder. It designates each quantized
level by a binary code. The sampling done here is the sample-and-hold process.
These three sections (LPF, Sampler, and Quantized) will act as an analog to digital
converter.Encodingminimizesthe bandwidthused.
o PCMtransmissionpath:-
RegenerativeRepeater
Thissectionincreasesthe signal strength.The outputof the channel alsohas
one regenerativerepeatercircuit,tocompensate the signal lossandreconstruct
7. the signal,andalsoto increase itsstrength. Here isthe blockdiagramof
regenerativefilter.
o PCMreceiver:-
Decoder
The decodercircuitdecodesthe pulse codedwaveformtoreproduce the
original signal.Thiscircuitactsas the demodulator.
ReconstructionFilter
Afterthe digital-to-analogconversionisdone bythe regenerative circuitandthe
decoder,alow-passfilterisemployed,calledasthe reconstructionfiltertoget
back the original signal.
Application:-
o The PCM isusedinthe satellitetransmissionsystem.
o It isusedin space communication.
o It isusedin telephony.
o The compact disc (CD) isa recentapplicationof PCM.
Advantagesof PCMcommunication:-
o PCMprovideshighnoise immunity.
o It ispossible toregenerate the codedsignalalongthe transmissionpath.
o It ispossible tostore the signal.
Disadvantagesof PCMcommunication:-
o The encoding,decodingandquantizingcircuitryof PCMis complex.
o PCMrequiresalarge bandwidthascomparedto othersystems.
8. DIFFERENTIAL PULSE CODE MODULATION (DPCM)
For the samplesthatare highlycorrelated,whenencodedbyPCMtechnique,leave redundant
informationbehind. PCMrequiresalarge bandwidthascomparedtoothersystems. Toprocessthis
redundantinformationand tosave bandwidthDPCMis introduced.
Basic Elementsof DPCMcommunication:-
o DPCMtransmitter :-
The predictorproducesthe assumedsamplesfromthe previousoutputsof the
transmittercircuit.The inputtothispredictoristhe quantizedversionsof the input
signal.Predictorinputisthe sumof quantizeroutputandpredictoroutput.
o DPCM receiver:-
The predictorassumesa value,basedonthe previousoutputs.The inputgiventothe
decoderisprocessedandthatoutputis summedupwiththe outputof the predictor,to
obtaina betteroutput.
9. Advantagesof DPCMcommunication:-
o As the differencebetweenx(nT) andx*(nT) isbeingencodedandtransmittedbythe PCM
technique asmall differance voltageistobe quantizedandencoded,thiswill needless
numberof quantizationlevelsandhence lessnumberof bitstorepresentthem
o Thus signalingrate andbandwidthof aDPCMwill be lessthanthat of PCM
Disadvantagesof DPCMcommunication:-
o Highbit rate
o Practical usage is limited
o Need the predicator circuitto be used which is very complex
DELTA MODULATION
The type of modulation,where the samplingrate ismuchhigherandin whichthe step size after
quantizationisof a smallervalue Δ,sucha modulationistermedasdeltamodulation.
If Mk > Mk-1 take 1
If Mk < Mk-1 take 0
Basic Elementsof deltamodulation :-
o Transmitter :-
The predictorcircuitin DPCMisreplacedbya simple delaycircuitinDM.
From the above diagram, we have the notationsas−
x(nTs)=oversampledinput
ep(nTs)=summeroutputandquantizerinput
eq(nTs) =quantizeroutput= v(nTs)v(nTs)
xˆ(nTs) = outputof delaycircuit
u(nTs) = inputof delaycircuit
10. o Receiver:-
From the above diagram,we have the notationsas –
vˆ(nTs) isthe inputsample
uˆ(nTs) isthe summeroutput
x¯(nTs) isthe delayedoutput
A binary sequence will be givenasan inputtothe demodulator.The stair-case
approximatedoutputisgiventothe LPF.
Advantage :-
o Since.Deltamodulationtransmit1bit forone sample,thereforethe signalingrate and
transmissionbandwidthisquite small.
o Very easydesignof the modulatorandthe demodulator
Disadvantage :-
o If signal changesveryfast“overloadslope noise”occurs.
o If signal changesveryslow“granularnoise”occurs.
ADDAPTIVE DELTA MODULATION
In orderto overcome the quantizationerrors due toslope overloadandgranularnoise,the stepsize (Δ)
ismade adaptive tovariationsinthe inputsignal x(t).Particularlyinthe steepsegmentof the signal x(t),
the stepsize isincreased.Andthe stepisdecreasedwhenthe inputisvaryingslowly.Thismethodis
knownas Adaptive DeltaModulation(ADM).The adaptive deltamodulatorscantake continuous
changesinstepsize or discrete changesinstepsize.
11. Basic Elementsof deltamodulation:-
o Transmitter :-
The logicfor step size control isaddedinthe diagram.The stepsize increasesor
decreasesaccordingtoa specifiedrule dependingonone bitquantizeroutput.
o Receiver:-
The receiverhastwoportions.The firstportionproducesthe stepsize fromeach
incomingbit.Exactlythe same processisfollowedasthatintransmitter.The previous
inputandpresentinputdecide the stepsize.Itisthenappliedtothe secondportioni.e.,
an accumulatorwhichbuildsupstaircase waveform.The low passfilterthensmoothens
out the staircase waveformtoreconstructthe original signal.
Advantages:-
o The signal to noise ratioof ADMis betterthanthat of DM because of the reductionin
slope overloaddistortionandidle noise.
o Because of the variable stepsize ,the dynamicrange of ADM is widerthanDM.
o Utilizationof bandwidthisbetterinADMthan DM.
12. Disadvantages :-
o Implementationof stepsize control logiccircuitisnoteasy.
COMPARISONBETWEEN PCM, DELTA MODULATION, ADAPTIVE DELTA MODULATION AND
DEFFERENTIAL PULSE CODE MODULATION
DIFFERENCES BETWEEN WAVEFORMCODING AND SOUCECODING :-
The waveformcodersare generallydesignedtobe signal independent.
The waveformcodersare differentfromthe sauce coders.The source codersdependon
parameterizationof the analogsignal inaccordance withan appropriate model forgenerationof
signal.
REFERENCES :-
https://electronicspost.com
https://www.quora.com
https://www.tutorialpoint.com
https://www.wikipedia.com