Sampling a Continuous-Time Signal

Spectrum of a sampled signal with aliases shown

The signals of our interest — wireless communication waveforms — are continuous-time as they have to travel through a real wireless channel. To process such a signal using digital signal processing techniques, the signal must be converted into a sequence…
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Dealing with Complex Numbers

A complex number with its I and Q components

Although complex notation is not complex to understand (see Chapter 8 in Understanding Digital Signal Processing by Richard Lyons for an excellent tutorial), one of the themes of this text is to avoid complex notation altogether. A complex number is…
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What is a Signal?

A signal composed of the words "hello wireless"

A signal is any measurable quantity that varies with time (or some other independent variable). If you record the words you speak in a computer memory and plot against time, you get a speech signal. As an example, the above…
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Computing Error Rates

Spectral efficiency R_b/B versus E_b/N_0 determines the overall merit of a modulation scheme. This figure is drawn for BER = 10^{-5} and a Square-Root Raised Cosine pulse with 50% excess bandwidth

Having built a simple digital communication system, it is necessary to know how to measure its performance. As the names say, Symbol Error Rate (SER) and Bit Error Rate (BER) are the probabilities of receiving a symbol and bit in…
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