Digital Communications 0909.402.03/0909.504.01 Fall 2002 Lecture 6 October 14, 2002 Shreekanth Mandayam ECE Department Rowan University http://engineering.rowan.edu/~shreek/fall02/digcomm/

Plan Baseband Data Transmission Recall: Detection in the presence of AWGN Receiver Model Matched Filter Detector BER for Unipolar and Bipolar Signaling BER for multilevel signaling Correlation receiver Bandlimited Channels and ISI Pulse Shaping: Raised Cosine Response Eye Diagrams

Digital Communications Transceiver Anti- aliasing Filter Data Encryption Encoder Error Control Encoder Source Encoder Channel/ Line Encoder Sampling Quantization MUX Modulator ADC Analog i/p CODEC MODEM Multiple access channel Analog o/p Data Encryption Decoder Error Control Decoder Audio Amp Reconstruction/ DAC Source Decoder Equalization / Decision Circuits DEMUX Demod-ulator

Recall: Receiver Model TX S s(t) n(t) LPF Comparator r(t) t=t0 VT m ~ r0(t) r0(t0) m

Recall: Multilevel Signaling Binary Source l-bit DAC Binary signal D symbols/second = R bits/second L=2l Multilevel Signal D symbols/second = R/l R bits/second 0 1 2 3 4 5 6 7 8 4 2 -2 -4 Tb Ts T0 t (ms)

Average Symbol Error demos/BER_multilevel_baseband.m

Matched Filter/Correlation Receiver s(t) Matched Filter h(t) r0(t) = s0(t) + n0(t) r(t) = s(t) + n(t) A T s(-t) A -T h(t)=s(T-t) X s(t) Integrator t=t0 r0(t) r0(t0) s(t) + n(t) A T h(t)*s(t) A2 T 2T t=t0=T

Bandlimited Channels: Inter-Symbol Interference (ISI) Band-unlimited Channel f H(f) Input pulse Output pulse t t Transmission Channel Band-limited Channel Output pulse Input pulse H(f) -B B f t t

Pulse Shaping: Nyquist’s First Method for Zero ISI HE(f) Transmit Filter HT(f) Channel Characteristics HC(f) Receiver Filter HR(f) vi(t) v0(t) t t 1 0 1 1

Pulse Shaping: The Raised Cosine Response He(f) fD fD 1.0 0.5 -B -f0 -f1 f1 f0 B f

Pulse Shaping: The Raised Cosine Response he(t) 2f0 t -3/2f0 -2/2f0 -1/2f0 1/2f0 2/2f0 3/2f0

Summary