1. Oct 14, 2005CS477: Analog and Digital Communications1 Noise in Baseband Analog Systems Analog and Digital Communications Autumn 2005-2006

2. Oct 14, 2005CS477: Analog and Digital Communications2 Noise White Noise Filtered/Colored Noise LPF Power in filtered noise increases with filter bandwidth

3. Oct 14, 2005CS477: Analog and Digital Communications3 Noise Equivalent Bandwidth Average power in filtered noise: (Noise equivalent bandwidth)

4. Oct 14, 2005CS477: Analog and Digital Communications4 Baseband Signals with Noise Baseband Signals Signals in which no carrier modulation is performed Baseband performance is usually used as reference for comparison. We will use it! Performance criteria for analog systems Signal-to-noise ratio (SNR) Performance criteria for digital systems Bit error rate (BER) and transmission rate

5. Oct 14, 2005CS477: Analog and Digital Communications5 Additive Noise Receiver Model (signal and noise uncorrelated) Linear Receiver Received Signal Additive Noise A baseband receiver (Subscript used for destination)

6. Oct 14, 2005CS477: Analog and Digital Communications6 Baseband Noisy Receiver How to measure the destination SNR? 1. Turn off signal and measure the output 2. Turn on signal and measure the output 3. Take the ratio

7. Oct 14, 2005CS477: Analog and Digital Communications7 Analog baseband noisy transmission 1. Destination noise power is proportional to filter bandwidth 2. A wideband signal suffers more from noise contamination LPF Additive Noise Fig: A baseband noisy transmission model Loss (Destination noise power) (Upper bound on destination SNR)

8. Oct 14, 2005CS477: Analog and Digital Communications8 Use of Repeaters What if the destination SNR is below desired level? LPF Additive Noise Loss To next repeater USE A REPEATER!!! Improvement factor from no-repeater case: is the power loss incurred in each section