1. Nov 01, 2005CS477: Analog and Digital Communications1 Bandpass Noise Analog and Digital Communications Autumn 2005-2006

2. Nov 01, 2005CS477: Analog and Digital Communications2 CW Analog Systems Most analog continuous-wave systems are bandpass systems and suffer from bandpass noise (also a bandpass signal!) is additive white gaussian noise (AWGN) Detector Additive Noise BPF LPF CW modulated signal at receiver front end

3. Nov 01, 2005CS477: Analog and Digital Communications3 Bandpass Noise First deal with noise only. Turn the signal OFF… is bandpass noise What is It is colored and has finite power Let the bandpass filter for positive frequencies is: DSB: USSB: LSSB:

4. Nov 01, 2005CS477: Analog and Digital Communications4 Bandpass Noise Predetection Bandpass noise spectrum is predetection noise is predetection noise power is transmission bandwidth, not the message BW High transmission bandwidth means more predetection noise

5. Nov 01, 2005CS477: Analog and Digital Communications5 Predetection SNR For baseband transmission, we defined: Therefore, for passband transmission: is an upper bound on SNR because

6. Nov 01, 2005CS477: Analog and Digital Communications6 Quadrature decomposition of Noise is predetection bandpass noise has noise eq. BW equal to transmission BW are jointly stationary and gaussian Properties of quadrature components (prove at home!): What are the spectral properties of quadrature components? Note: quadrature components are lowpass signals!

7. Nov 01, 2005CS477: Analog and Digital Communications7 PSD of Quadrature Components (prove it at home: see page 405 and example 9.2-3) Type of modulation dictates Noise power can be easily computed for all types of Modulation because:

8. Nov 01, 2005CS477: Analog and Digital Communications8 Noise: Envelope and Phase (complementary cdf) is Rayleigh distributed is Uniform (power in noise envelope)