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CNU Dept. of Electronics D. J. Kim1 Lecture on Communication Theory Chapter 5. Noise in CW Modulation System 5.1 Introduction - Receiver Noise (Channel.

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Presentation on theme: "CNU Dept. of Electronics D. J. Kim1 Lecture on Communication Theory Chapter 5. Noise in CW Modulation System 5.1 Introduction - Receiver Noise (Channel."— Presentation transcript:

1 CNU Dept. of Electronics D. J. Kim1 Lecture on Communication Theory 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 T e = equivalent noise Temp. Average noise power per unit bandwidth S w (f) Rw()Rw() f 

2 CNU Dept. of Electronics D. J. Kim2 Lecture on Communication Theory - Band Pass Filter (Ideal case) w(t) n(t) - filtered noise as narrow-band noise n(t) = n I (t)cos(2  f C t) - n Q (t)sin(2  f C t) where n I (t) is inphase, n Q (t) is quadrature component -  filtered signal x(t) x(t) = s(t) + n(t) - Average Noise Power = N 0 B T BPF 2B N0N0 S NI, S NQ

3 CNU Dept. of Electronics D. J. Kim3 Lecture on Communication Theory - DSB - SSB 1 S M (f) f S S (f) f f S Y (f) f S S (f) f 1 f f ff

4 CNU Dept. of Electronics D. J. Kim4 Lecture on Communication Theory 2. 변복조간의 비교 1) 서로 다른 변복조 system 을 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 CNU Dept. of Electronics D. J. Kim5 Lecture on Communication Theory 2. (SNR) O

6 CNU Dept. of Electronics D. J. Kim6 Lecture on Communication Theory 5.4 Noise in SSB Receivers - SSB Modulated wave

7 CNU Dept. of Electronics D. J. Kim7 Lecture on Communication Theory

8 CNU Dept. of Electronics D. J. Kim8 Lecture on Communication Theory 5.4 Noise in AM Receiver

9 CNU Dept. of Electronics D. J. Kim9 Lecture on Communication Theory - By envelope detector ex1) Single-Tone Modulation

10 CNU Dept. of Electronics D. J. Kim10 Lecture on Communication Theory 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.

11 CNU Dept. of Electronics D. J. Kim11 Lecture on Communication Theory 5.6 Noise in FM Receivers w(t) : zero mean white Gaussian noise with psd = N o /2 s(t) : carrier =f c, BW = B T 즉 (f C  B T /2) - BPF : [f C - B T /2 ~ f C + B T /2] - Amplitude limiter : remove amplitude variations by clipping and BPF - Discriminator  slope network or differentiator : varies linearly with frequency  envelope detector - Baseband LPF : message BW 에 맞추어서. - FM signal - Filtered noise n(t)

12 CNU Dept. of Electronics D. J. Kim12 Lecture on Communication Theory - Discriminator output at discriminator output at Rx output

13 CNU Dept. of Electronics D. J. Kim13 Lecture on Communication Theory - Figure of merit of FM where P = message power W = message bandwidth k f = frequency sensitivity  B T Noise Performance ex) Single-tone modulation trade off

14 CNU Dept. of Electronics D. J. Kim14 Lecture on Communication Theory 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 band 를 효과적으로 사용 못함  Commercial FM radio 에서 사용 signal noise

15 CNU Dept. of Electronics D. J. Kim15 Lecture on Communication Theory Applications) FM radio, audio-tape-recording Dolby-A, Dolby-B, DBX : filtering+dynamic range compression

16 CNU Dept. of Electronics D. J. Kim16 Lecture on Communication Theory 5.8 Summary and Discussion chap chap , 6.7, 6.15, 6.17


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