Browsed by
Category: Fundamental Concepts

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

Understanding Noise – Part 4: Noise Factor, Noise Figure & Noise Temperature

Understanding Noise – Part 4: Noise Factor, Noise Figure & Noise Temperature

Previous posts in this series: Understanding Noise – Part 1: Defining Noise Understanding Noise – Part 2: Sources of Noise Understanding Noise – Part 3: Noise Spectral Density Digital communication systems require received signals to be filtered and amplified before they can be demodulated and passed to the analog to digital converter.  Similarly, transmitted signals must also be passed to an analog amplifier and filter before being transmitted.  These components insert additional noise into the transmitted/received signals, negatively affecting the…

Read More Read More

Understanding Noise – Part 3: Noise Spectral Density

Understanding Noise – Part 3: Noise Spectral Density

Previous posts in this series: Understanding Noise – Part 1: Defining Noise Understanding Noise – Part 2: Sources of Noise In this post I want to discuss Noise Spectral Density. Noise Spectral Density Noise Spectral Density or Noise Density, (No) is a measurement of the noise power per Hertz.  For white noise, which is constant with respect to frequency we can simply divide the total noise power by the bandwidth of the system.  Assuming that thermal noise is the predominant…

Read More Read More

Understanding Noise – Part 2: Sources of Noise

Understanding Noise – Part 2: Sources of Noise

Previous posts in this series: Understanding Noise – Part 1: Defining Noise Sources of Noise Thermal Noise The first major contributor to noise inside electronic components comes in the form of Thermal or Johnson-Nyquist Noise.  This noise is present even when there is no current actually passing through any component.  It is present even when the device is turned off! Thermal noise is caused by the random movements of electrons inside resistive electrical components.  A perfect capacitor or perfect inductor…

Read More Read More

Understanding Noise – Part 1: Defining Noise

Understanding Noise – Part 1: Defining Noise

One of the supposedly simple things that plagues me in communications theory is the idea of noise.  We are all very comfortable talking about noise.  We refer to noise, the noise floor and interference all the time quite glibly. Yet I must admit, I have always felt like I never truly understood the topic. In this post I want to take a deeper look at noise: its definition, where it comes from, its characteristics and how to measure it in modern…

Read More Read More

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,…

Read More Read More

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…

Read More Read More

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…

Read More Read More

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…

Read More Read More

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…

Read More Read More

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….

Read More Read More