ECE 4371, Fall, 2014 Introduction to Telecommunication Engineering/Telecommunication LaboratoryOverviewCo-channel InterferenceSystem Model and Noise ModelSignal after bandpass filterDiscriminator OutputNoise After DiscriminatorNoise After Discriminator cont.Slide 9SNR of FMSingle Tone FM SNRFM Preemphsis and DeemphasisSlide 13FM Threshold EffectExampleThreshold EffectComparison of modulation systemsComparison of the noise performance of various CW modulation systems. Curve I: Full AM, m = 1. Curve II: DSB-SC, SSB. Curve III: FM, b = 2. Curve IV: FM, b = 5. (Curves III and IV include 13-dB pre-emphasis, de-emphasis improvement..)EncryptionEncryption – cipher taxonomyTransposition MethodSubstitution MethodRotor MachineKeyPublic Key System - RSASlide 26Quantum CryptographyMission is really impossibleECE 4371, Fall, 2014Introduction to Telecommunication Engineering/Telecommunication Laboratory Zhu HanDepartment of Electrical and Computer EngineeringClass 6Sep. 15th, 2014OverviewOverviewCochannel interferenceAnalysis of Noise–Math model (good thing, not required)–Noise shape, preemphasis/deemphasis–FM threshold effectsSecurity basicsHomework 1 hintsGood news: This is the last class for exam 1Co-channel InterferenceCo-channel InterferenceSource: Acoswct, Interference: Icos(wc+w)tr(t)= Acoswct+Icos(wc+w)t=E(t)cos(wct+)=tan^-1(Isinwt/(A+Isinwt))~=(I/A)sinwtPM: y=(I/A)sinwt, FM =(Iw/A)coswtWhen A is large, suppress weak interference better than AM.Capture effect–Winner takes all–35dB for AM–6 dB for FM/PMWhite Gaussian noise–Noise increases linearly with frequency in FM.System Model and Noise ModelSystem Model and Noise ModelDiscriminator consists of a slope network and an envelope detector.Signal after bandpass filterSignal after bandpass filterThe incoming FM signal s(t) is defined byAt the bandpass filter outputDiscriminator OutputDiscriminator OutputNote that the envelope of x(t) is of no interest to us (limiter)  (2.141) )()( sin)( 21)( wheretttrdtd Atncd )138.2( )()(sin)()()()( BecausettAtrtttrAcc (2.139) )()(sin)()(20ttAtrdm kctfnoise additivemessage (2.140) )()( )(21)(2.40) (Fig isoutput tor discrimina ThetntmkdttdtvdfNoise After DiscriminatorNoise After Discriminator  (2.142) )(sin)(21)( ttrdtd Atncd (2.143) )(sin)()( have we, )( and )( of definition FromttrtnttrQ(2.144) )(21)(dttdn AtnQcd as )(simplify may Wesignal. message oft independen is )(then ),2 (0,over ddistributeuniformly is )()( AssumetntnttddThe quadrature appearsNoise After Discriminator cont.Noise After Discriminator cont.The average output signal power = kf2P Recall fjdtdTF2.nQ(t) nd(t)dtd Ac21)( fSQN)( fSdN(2.145) )()(22fSAffSQdNcNNoise After Discriminator cont.Noise After Discriminator cont.Assume that nQ(t) has ideal low-pass characteristic with bandwidth BT(2.146) 2 , )(220 TcNBfAfNfSd(2.147) , )( output receiver At the 2 If2200WfAfNfSWBcNTSNR of FMSNR of FMeffect quieting noise 1 (2.148) 32 )( ofpower Average2230 2200ccWWcAAWNdffANtn(2.149) 23)SNR(3022FM,WNPkAfcO(2.150) 2)SNR( isbandwidth messagein power seaveragenoi the,2 is )( ofpower average The02FM,02WNAWNAtscCc(2.151) 3)SNR()SNR(22FMWPkfCO71Single Tone FM SNRSingle Tone FM SNR )2sin(2cos)( t ffft fAtsmmcc 2.4) Example (from 31)SNR()NR( , AM tocompareCOAMS)2cos()( sideboth )2sin()(2 , may write We0t fkftmdtdt fffdm kmfmmtf222)( is load) 1 (across )( ofpower average ThefkfPtmWNAWNfAccO0223022FM,43 4)(3)SNR( (2.149), From(2.152) 23)(23)SNR()SNR(22FMWfCOFM. widebandand FM narrowbandbetween n transitio theas 5.0 Define471.032 e.performancbetter has FM , 31 23When 2FM Preemphsis and DeemphasisFM Preemphsis and DeemphasisFM Preemphsis and DeemphasisFM Preemphsis and DeemphasisFM Threshold EffectFM Threshold Effect 2)( toequal isoutput tor discrimina The2 decreasesor increases (t),origin thearound sweepmay ly,Occasional)()(tan)((2.153) )2sin()()2cos()()(input tor discriminafrequency at the signal composite The d.unmodulate iscarrier i.e., signal, no is When there' 11tPtnAtntt ftnt ftnAtxIcQcQcIcnQ(t)r(t)x(t)Ac(t)P10P2nI(t)ExampleExampleIllustrating impulse ike components in  (t)  d(t)/dt produced by changes of 2 in  (t); (a) and (b) are graphs of  (t) and  (t), respectively.Threshold EffectThreshold EffectDependence of output signal-to-noise ratio on input carrier-to-noise ratio for FM receiver. In curve I, the average output noise power is calculated assuming an unmodulated carrier. In curve II, the average output noise power is calculated assuming a sinusoidally modulated carrier. Both curves I and II are calculated from theory.Comparison of modulation systemsComparison of modulation systemsComparison of the noise Comparison of the noise performance of various performance of various CW modulation systems. CW modulation systems. Curve I: Full AM, Curve I: Full AM, = 1. = 1. Curve II: DSB-SC, SSB. Curve II: DSB-SC, SSB. Curve III: FM, Curve III: FM, = 2. = 2. Curve IV: FM, Curve IV: FM, = 5. = 5. (Curves III and IV include (Curves III and IV include 13-dB pre-emphasis, de-13-dB pre-emphasis, de-emphasis improvement..)emphasis improvement..)EncryptionEncryptionEncryption is a translation of data into a secret code. Encryption is the most effective way to achieve data security. To read an encrypted file, you must have access to a secret key that enables you to decrypt it. Unencrypted data is called plain text; encrypted data is referred to as cipher (text).Encryption can be used to ensure secrecy, but other techniques are still needed to make communications secure: authentication, authorization, and message integrity.–Message integrity - both parties will always wish to be confident that a message has not been altered during transmission. The encryption makes it difficult for a third party to read a message, but that third party may still be able to alter it in a