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Chapter 5. Noise in CW Modulation System

S w (f). f. R w (  ). . Chapter 5. Noise in CW Modulation System. 5.1 Introduction - Receiver Noise (Channel Noise) : additive, White, and Gaussian 으로 가정 5.2 Receiver Model 1. RX Model N 0 = KT e where K = Boltzmann’s constant

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Chapter 5. Noise in CW Modulation System

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  1. Sw(f) f Rw()  Chapter 5. Noise in CW Modulation System • 5.1 Introduction • - Receiver Noise (Channel Noise) : • additive, White, and Gaussian 으로 가정 • 5.2 Receiver Model • 1. RX Model • N0 = KTe where K = Boltzmann’s constant • Te = equivalent noise Temp. • Average noise power per unit bandwidth

  2. SNI, SNQ N0 BPF 2B • - Band Pass Filter (Ideal case) • w(t) n(t) • - filtered noise as narrow-band noise • n(t) = nI(t)cos(2fCt) - nQ(t)sin(2fCt) • where nI(t) is inphase, nQ(t) is quadrature component • -  filtered signal x(t) • x(t) = s(t) + n(t) • - Average Noise Power = N0BT 2B

  3. SY(f) SM(f) SS(f) 1 f f f SS(f) f f 1 f f f f < DSB와 SSB의 Signal과 Noise Power Spectral Density 정리 > - DSB - SSB

  4. 2. 변복조간의 비교 • 1) 서로 다른 변복조 system을 비교하기 위한 조건 • - s(t) by each system has the same average power • - noise w(t) has the same average power measured in the message • BW =W • 2) Channel SNR • 3) • 5.3 Noise in DSB-SC Receivers • 1. Model of DSB-SC Receivers

  5. 2. (SNR)O

  6. 5.4 Noise in SSB Receivers • - SSB Modulated wave

  7. 5.4 Noise in AM Receiver

  8. - By envelope detector • ex1) Single-Tone Modulation

  9. Threshold Effect • Carrier-to-noise < 1 • narrow-band noise n(t) • Threshold Effect : loss of message in an envelope detector that • operates at a low CNR.

  10. 5.6 Noise in FM Receivers • w(t) : zero mean white Gaussian noise with psd = No/2 • s(t) : carrier =fc, BW = BT즉 (fC BT/2) • - BPF : [fC -BT/2 ~ fC +BT/2] • - Amplitude limiter : remove amplitude variations • by clipping and BPF • - Discriminator • slope network or differentiator : varies linearly with frequency • envelope detector • - Baseband LPF : message BW에 맞추어서. • - FM signal • - Filtered noise n(t)

  11. - Discriminator output at discriminator output at Rx output

  12. - Figure of merit of FM • where P = message power • W = message bandwidth • kf = frequency sensitivity • <결론> BT Noise Performance • ex) Single-tone modulation trade off

  13. 5.7 Pre-emphasis and de-emphasis in FM • P.S.D. of noise at FM Rx output • P.S.D. of typical message signal • => 모든 band를 효과적으로 사용 못함 • Commercial FM radio에서 사용 signal noise

  14. Applications) FM radio, audio-tape-recording • Dolby-A, Dolby-B, DBX : filtering+dynamic range compression

  15. 5.8 Summary and Discussion <H.W.> chap 5. 5.7 chap 6. 6.2, 6.7, 6.15, 6.17

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