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Category: Fundamental Concepts

All posts covering the fundamental concepts applicable to wireless communications in general.

Sampling

Sampling

One of the most commonly misunderstood aspects of signal processing is the Nyquist-Shannon Sampling Theorem.  It has been noted before that many engineers misunderstand the theorem, selecting sampling frequencies that are often too low, causing errors in systems design.   An understanding of the underlying theory behind signal sampling is also useful to the communications engineer who wants a deeper understanding of the application of analog and digital filtering and information processing in communications equipment. The Need for Sampling Sampling analog,…

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Passband Signals

Passband Signals

The term Passband signal in the current context refers to the modulated signal that results from a baseband signal modulating a carrier wave.  Passband signals have some interesting characteristics that we will cover by referring to the diagrams below. (Disclaimer: illustrative purposes only). Properties of Passband Signals Shifted Frequency Response The complete frequency response (including both positive frequencies and negative frequencies) of the baseband signal is preserved in the passband signal, but is now centered around the positive and negative…

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Filters

Filters

Signal filtering plays a fundamental role in electronics and communications.  Filters modify specific frequency components of time-domain signals and are used as a tool for signal quality improvement, information recovery and frequency separation [1].  Filters are a fundamental frequency domain tool and as a component in electronic circuits and digital signal processing allow us to: Isolate circuits from DC (0Hz) currents. Suppress high and low frequency noise in received signals. Improve the spectral efficiency of transmitted signals. Separate the frequency…

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Baseband Signals

Baseband Signals

The difference between the baseband signal and the passband signal in communications is really quite a simple one.  The baseband signal refers to any signal that has not modulated a carrier waveform. NOTE:  The use of the verb “modulated” there may made you think twice.  If so, you are not alone.  I always used to think that the carrier waveform was the object that acted on our baseband signal.  This is the wrong way to think of it.  The process…

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Fourier Transform

Fourier Transform

The Frequency Domain Many physical objects have a frequency range over which they perform most of their work.  Your ears for instance, can generally only hear frequencies between 20Hz and 20 kHz.  Your own voice when speaking normally, concentrates most power in the range of 500 to 2000Hz.  You can think of these as the bandwidth of their operation.  Other real world sources have their own bandwidths of operation.  A tuning fork has a very narrow bandwidth tuned to a…

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High Level Components of a Digital Wireless Communications System

High Level Components of a Digital Wireless Communications System

A Simple Model What does a digital communications link actually look like? This is a useful question to answer as it gives us a model we can continuously refer back to as we learn more about communications.  Having a model means that when things get confusing later on, we can go back and see which technique, technology or innovation fits where.  A simplistic model of a communications link is shown below, consisting of a source, transmitter, channel, receiver and destination….

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