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 

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

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

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

CNU Dept. of Electronics D. J. Kim5 Lecture on Communication Theory 2. (SNR) O

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

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

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

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

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.

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)

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

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

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

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

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