# S. Mandayam/ ECOMMS/ECE Dept./Rowan University Electrical Communications Systems ECE.09.331 Spring 2010 Shreekanth Mandayam ECE Department Rowan University.

## Presentation on theme: "S. Mandayam/ ECOMMS/ECE Dept./Rowan University Electrical Communications Systems ECE.09.331 Spring 2010 Shreekanth Mandayam ECE Department Rowan University."— Presentation transcript:

S. Mandayam/ ECOMMS/ECE Dept./Rowan University Electrical Communications Systems ECE.09.331 Spring 2010 Shreekanth Mandayam ECE Department Rowan University http://engineering.rowan.edu/~shreek/spring10/ecomms/ Lecture 13a April 20, 2010

S. Mandayam/ ECOMMS/ECE Dept./Rowan UniversityPlan 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 Bit Error Rates (BERs) for Digital Comm. Sys. General Procedure M-ary PSK and M-ary QAM Output SNR for Analog Comm. Sys. AM, DSB-SC, SSB and FM

S. Mandayam/ ECOMMS/ECE Dept./Rowan University ECOMMS: Topics

S. Mandayam/ ECOMMS/ECE Dept./Rowan University Performance of Communications Systems Corrupted by Noise Digital Bit Error Rate (BER) Analog Output SNR

S. Mandayam/ ECOMMS/ECE Dept./Rowan UniversityNoise A random, unwanted fluctuation in signal amplitude Thermal (Johnson) Noise Amplitude vs. time: Gaussian PDF Model See Lab1 Pre-lab Lecture: lab1.pptlab1.ppt We also want to know how much noise power there is per Hz – why?

S. Mandayam/ ECOMMS/ECE Dept./Rowan UniversityWhy? f |W(f)| Baseband 0 f |W(f)| Bandpass 0 fcfc -f c f |W(f)| Bandpass 0 f IF -f IF 1. Modulation 2. Demodulation 3. Demodulation

S. Mandayam/ ECOMMS/ECE Dept./Rowan University 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

S. Mandayam/ ECOMMS/ECE Dept./Rowan University Autocorrelation Function Measure of similarity of a waveform observed at times  seconds apart how rapidly a random waveform fluctuates with time 0 Rx()Rx()  (time delay) Slowly fluctuating signal rapidly fluctuating signal R w (  ) P w (f) F Wiener-Khintchine Theorem Matlab Demo: autocorr.m

S. Mandayam/ ECOMMS/ECE Dept./Rowan University Thermal (Johnson) Noise 00.511.522.53 x 10 12 0 0.5 1 1.5 2 x 10 -21 PSD of thermal noise frequency, Hz PSD, W/Hz Matlab script: psd_noise.m

S. Mandayam/ ECOMMS/ECE Dept./Rowan University Digital Communications System Modulated Signal s(t) Digital Output Noise w(t) Sample & Hold  + + Noisy Receiver Model Processing Threshold

S. Mandayam/ ECOMMS/ECE Dept./Rowan University Symbol Error in M-ary PSK Systems Matlab script: dignoise.m

S. Mandayam/ ECOMMS/ECE Dept./Rowan University Symbol Error in M-ary QAM Systems Matlab script: dignoise.m

S. Mandayam/ ECOMMS/ECE Dept./Rowan University Analog Communications Systems BPF Modulated Signal s(t) Output (Signal + Noise) Noise n(t) Demodulator  + + Noisy Receiver Model LPF Message Signal m(t) Baseband Output (Signal+ Noise) Noise n(t)  + + Baseband Model

S. Mandayam/ ECOMMS/ECE Dept./Rowan University Output SNR in Analog Comm. Systems Matlab script: analognoise.m

S. Mandayam/ ECOMMS/ECE Dept./Rowan UniversitySummary

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