10-401-06-BasebandTransmissionDetection-1

10-401-06-BasebandTransmissionDetection-1 - Essential...

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Baseband Transmission 1 EE 401/522 Digital Communications Essential Blocks:Digital Communication System Format Pulse Modulation Bandpass Modulation Transmitter Synchronization Format Detection Demodulation Sampling Receiver Channel 010100 0 T 2T 3T 4T 5T 6T 7T 8T 0 T 2T 3T 4T 5T 6T 7T
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Baseband Transmission 2 EE 401/522 Digital Communications Problem Description voltage Time Time Time transmitted signal g t noise w t received signal x t Σ
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Baseband Transmission 3 EE 401/522 Digital Communications Receiver(demodulator) design In addition to noise (AWGN), there are intersymbol interference (ISI) distortion Develop a method to extract the transmitted signal from the noisy received signal Illustration of ISI for baseband waveforms
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Baseband Transmission 4 EE 401/522 Digital Communications Baseband demodulator Objective is to extract the transmitted signal, not in the form of ideal pulse shapes suffer from ISI ( intersymbol interference ) due to filtering in the transmitter and in the channel distorted in the channel The demodulator aims to recover a baseband pulse with best SNR make pulses free of any ISI Consider only noise corruption (in this course): “Performance of digital modulation schemes under AWGN channel”
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Baseband Transmission 5 EE 401/522 Digital Communications Receiver structure: filtering+sampling Linear Time Invariant (LTI) filter Σ h t signal g t w t x t = g t  w t y T sample at t = T w t : white noise S w f = PSD = N 0 / 2 W / Hz y t = g 0 t  n t Design an optimum filter h t or H f  making output SNR maximum: = g 0 T ∣ 2 E [ n 2 t ] g 0 T ∣ 2 : instantenous signal power E [ n 2 t ] : average noise power at the output E : expectation operator
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6 EE 401/522 Digital Communications Design: Matched filter (MF) Transform pairs: g t  G f h t  H f g 0 t  G 0 f n t  S N f Without input noise: g 0 t = g t * h t G 0 f = G f H f g 0 t = FT 1 [ G 0 f ]= −∞ G f H f e j2 f t df filter output sampled at t = T g 0 T ∣ 2 =∣ −∞ G f H f e j2 f T df 2 With only input noise: n t = w t * h t S N f = S W f ∣ H f ∣ 2 Average power of the output noise E [ n 2 t ]= −∞ S N f df = N 0 2 −∞ H f ∣ 2 df = = g 0 T ∣ 2 E [ n 2 t ] = −∞ G f H f e j2 f T df 2 N 0 2 −∞ H f ∣ 2 df Problem: find an H f such that makes a maximum for a given G f ? Linear Time
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This note was uploaded on 12/15/2010 for the course EE EE 401 taught by Professor Alikara during the Spring '10 term at Ankara Üniversitesi.

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10-401-06-BasebandTransmissionDetection-1 - Essential...

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