A Digital Communication System

Quadrature Amplitude Modulation (QAM)

A general QAM detector with respective waveforms at each block

We discussed earlier that Pulse Amplitude Modulation (PAM) transmits information through amplitude scaling of the pulse according to the symbol value. To understand QAM, we have to differentiate between baseband and passband signals. A baseband signal has a spectral magnitude…
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A Simple Communication System

Blocks of a simple binary communication system

In every digital communication system, whether it is a home DSL or cellular data plan, one fundamental parameter we always hear about is the data rate. Data rate is simply the number of bits transmitted and received during one second,…
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Tools for Signal Diagnosis

All symbol intervals are overlayed on top of one another and the time axis is shifted to bring ideal sampling instant in the middle. Eye diagram generated for 250 2-PAM symbols and Square-Root Raised Cosine pulse with excess bandwidth 0.5

We are now in a position to devise some tools that help us diagnose problems with the communication system under study. I like to call them the stethoscopes for a communications system due to the crucial functionality they provide regarding…
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Modulation – From Numbers to Signals

A rectangular pulse scaled by two amplitude levels, +A and -A

The purpose of digital communications is to send digital data across a channel which can be wireless telephone lines coaxial cable optical fiber Ethernet USB chips on a printed circuit board Considering the examples shown in Figure above, clearly neither…
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What is Communications?

Wired and wireless channels

"The fundamental problem of communication is that of reproducing at one point either exactly or approximately a message selected at another point." Claude Shannon – A Mathematical Theory of Communication Our main purpose is to transfer digital information – which…
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