pulse shaping

pulse shaping - 2007 BG Mobasseri ECE 3770 1 PULSE SHAPING...

Info iconThis preview shows pages 1–11. Sign up to view the full content.

View Full Document Right Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: 2007 BG Mobasseri ECE 3770 1 PULSE SHAPING 2007 BG Mobasseri ECE 3770 2 What is the problem? What we just went through was about picking a pulse sequence . We have not said anything about pulse shapes that make up the sequence. Square pulses are by no means the best shapes to use. 2007 BG Mobasseri ECE 3770 3 Criterion for picking pulse shapes Whatever line coding you choose, the shape of the pulse greatly affects signal properties. The two we are most concerned with are Bandwidth Interference with adjacent pulses 2007 BG Mobasseri ECE 3770 4 ISI: intersymbol interference Modern communication systems are mostly interference limited, not noise limited ISI is a phenomenon in digital signaling that arises from the interaction of the signal and communication channel 2007 BG Mobasseri ECE 3770 5 How is ISI created? There are a variety of reasons (bandlimited channels, multipath, fading). The end result is something like this 1 0 0 0 1 0 0 0 1 0 1 0 1 0 0 0 ISI causes detection error 0s may look like 1s and vice versa transmitted received 2007 BG Mobasseri ECE 3770 6 A note on notation We frequently talk about data rate either in terms of bits/sec(R b ) or pulses/sec(R). They are not the same because one pulse may represent several bits. Similarly, we may talk about bit length (T b =1/ R b ) or pulse width(T=1/R) We will use bit notations but results are applicable to pulses as well 2007 BG Mobasseri ECE 3770 7 Bandlimiting effect Take square NRZ pulses at R b bits/sec. The nominal pulse bandwidth is then R b Hz. Channel bandwidth must then be R b Hz. Nyquist said it should be possible to use only R b /2 Hz. Would a square pulse work? 1/R b ? H(f) R b /2 2007 BG Mobasseri ECE 3770 8 Output in the frequency domain In the frequency domain, input is a sinc. Rb R b transmit receive Rb/2 Clearly, the received pulse is severely bandlimited compared to its original shape. How does it look like in time? 2007 BG Mobasseri ECE 3770 9 Distorted pulse in time=pulse dispersion As a result of bandlimiting, we witness pulse dispersion, i.e. spreading transmitted received Tb/2 Tb time 2007 BG Mobasseri ECE 3770 10 Notion of sampling instant A digital receiver works on the basis of samples taken at periodic intervals....
View Full Document

Page1 / 41

pulse shaping - 2007 BG Mobasseri ECE 3770 1 PULSE SHAPING...

This preview shows document pages 1 - 11. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online