1. Electrical Communications Systems ECE.09.433
Noise I
Dr. Shreek Mandayam
Electrical & Computer Engineering
Rowan University

2. Plan Performance of Comm. Systems corrupted by Noise
Performance Measures: Digital and Analog
Thermal (Johnson) Noise
Amplitude: Recall Random Variables: lab1.ppt
Power Spectral Density
Autocorrelation function
Wiener-Khintchine Theorem

3. ECOMMS: Topics

4. Performance of Communications Systems Corrupted by Noise
Digital
Bit Error Rate (BER)
Analog
Output SNR

5. Noise A random, unwanted fluctuation in signal amplitude
Thermal (Johnson) Noise
Amplitude vs. time: Gaussian PDF Model
See Lab1 Pre-lab Lecture: lab1.ppt
We also want to know how much noise power there is per Hz – why?

6. Why? 2. Demodulation 1. Modulation 3. Demodulation f |W(f)| Bandpassfc
-fc
1. Modulation
2. Demodulation f
|W(f)|
Baseband f
|W(f)|
Bandpass
fIF
-fIF
3. Demodulation

7. Power Spectral Density (PSD)
Normalized power of a waveform in the frequency domain
Used for measuring signal/noise power loss/transfer in communications system blocks

8. Autocorrelation Function
Measure of
similarity of a waveform observed at times t seconds apart
how rapidly a random waveform fluctuates with time
Rx(t)
t (time delay)
Slowly
fluctuating signal
rapidly
Matlab Demo:
autocorr.m
Wiener-Khintchine Theorem
Rw(t) Pw(f) F

9. Thermal (Johnson) Noise
0.5 1
1.5 2
2.5 3
x 10 12
-21
PSD of thermal noise
frequency, Hz
PSD, W/Hz
Matlab script:
psd_noise.m

10. Summary