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S. Mandayam/ ECOMMS/ECE Dept./Rowan University Electrical Communications Systems ECE.09.331 Spring 2008 Shreekanth Mandayam ECE Department Rowan University http://engineering.rowan.edu/~shreek/spring08/ecomms/ Lecture 13b April 23, 2008

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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 Broadcast Transmitters and Receivers AM Broadcast Transmitter Class-C Amp Collector Modulator TRF Receiver Superheterodyne Receiver

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

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

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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?

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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

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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

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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

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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

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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

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

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

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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

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

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

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S. Mandayam/ ECOMMS/ECE Dept./Rowan University AM Broadcast Transmitter Temp. Stabilized Crystal Oscillator Buffer Amplifier Class-C Modulated Power Amp. Stage Class-C Modulated Power Amp. Stage Impedance Matching Network Audio Amplifier Modulator Driver Amplifier Demodulator Audio Input + -

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S. Mandayam/ ECOMMS/ECE Dept./Rowan University Amplifier Classification icic tt icic tt icic tt icic tt Class A Class B Class AB Class C

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S. Mandayam/ ECOMMS/ECE Dept./Rowan University BJT Collector Modulator Circuit Output Characteristics

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S. Mandayam/ ECOMMS/ECE Dept./Rowan University Circuit Operation BJT Collector Modulator

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S. Mandayam/ ECOMMS/ECE Dept./Rowan University AM Receiver Purpose Demodulate received signal Requirements Carrier frequency tuning Filtering Amplification

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S. Mandayam/ ECOMMS/ECE Dept./Rowan University Tuning Circuits Series Tuned Circuit + - V r C L I

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S. Mandayam/ ECOMMS/ECE Dept./Rowan University Series Tuned Circuit function [f,A]=resonance(f0,Q) %ECOMMS Spring 08 Class Demo %S. Mandayam, ECE Dept., Rowan University %To illustrate series resonance and Q-factor close all; %defining frequency axis f=f0-f0/2:0.1:f0+f0/2; %calculating relative response y=(f/f0)-(f0./f); A=20*log10(1./(1+(y*Q).^2).^0.5); plot(f-f0,A);grid on; xlabel('Shift from resonant frequency in Hz'); ylabel('Relative Response in dB'); title('Series Tuning Circuit');

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S. Mandayam/ ECOMMS/ECE Dept./Rowan University Tuning Circuits Parallel Tuned Circuit + - V r C L I Active Tuned Circuits?

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S. Mandayam/ ECOMMS/ECE Dept./Rowan University Tuned Radio Frequency (TRF) Receiver Active Tuning Circuit Detector Circuit Local Oscillator Bandpass Filter Baseband Audio Amp

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S. Mandayam/ ECOMMS/ECE Dept./Rowan UniversityHeterodyning Heterodyning (Upconversion/ Downconversion) Subsequent Processing (common) All Incoming Frequencies Fixed Intermediate Frequency

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S. Mandayam/ ECOMMS/ECE Dept./Rowan University Superheterodyne Receiver RF Amplifier H 1 (f) Mixer Local Oscillator IF Amplifier H 2 (f) Detector Audio Amp Common tuning f RF or f c f LO f IF fmfm fmfm Downconversion f IF = |f RF - f LO | Upconversion f IF = f RF + f LO

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

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