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

2. Nov 01, 2005CS477: Analog and Digital Communications2 Noise: Envelope and Phase (complementary cdf) is Rayleigh distributed is Uniform (power in noise envelope)

3. Nov 01, 2005CS477: Analog and Digital Communications3 Noise: Cross-correlation We noticed that: What about general cross-correlation? For local symmetry around the carrier, quadrature components of noise are uncorrelated and hence independent!

4. Nov 01, 2005CS477: Analog and Digital Communications4 Linear Modulation with Noise Answer: We are interested in postdetection SNR and this analysis is used for finding postdetection noise… What does the detector do? What is its output? Why did we analyze the following? 1. Quadrature decomposition of predetection noise 2. Envelope and phase of predetection noise Questions? 1. What is output (destination) SNR? 2. What is the output signal?

5. Nov 01, 2005CS477: Analog and Digital Communications5 Linear Modulation with Noise System Model Review: Detector BPF LPF Need to evaluate: What are the in-phase and quadrature components of predetection signal and noise and what type of detector is used with what type of modulation?

6. Nov 01, 2005CS477: Analog and Digital Communications6 Synchronous Detection DSB case: (LPF is ideal)

7. Nov 01, 2005CS477: Analog and Digital Communications7 Synchronous Detection AM signal: (ideal LPF+DC block)

8. Nov 01, 2005CS477: Analog and Digital Communications8 Synchronous Detection AM signal: AM signal with full-load tone modulation:

9. Nov 01, 2005CS477: Analog and Digital Communications9 Synchronous Detection SSB signal:

10. Nov 01, 2005CS477: Analog and Digital Communications10 Envelope Detection of AM With large SNR: (Similar to synchronous detection) With small SNR: Signal mutilation and Threshold Effect Threshold effect not so serious in AM systems

11. Nov 01, 2005CS477: Analog and Digital Communications11 Noise in Exponential Modulation PM and FM Noise Predetection Signal UP, noise DOWN  Noise Quieting

12. Nov 01, 2005CS477: Analog and Digital Communications12 Noise in Exponential Modulation Signal-to-noise ratio: See Table 10.4-1 page 423 of text!