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# System prepended metadata

title: RF Engineering

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# RF Engineering
[TOC]
## Channel Definition
The received signal y(t) can be defined as the result of the convolution between the transmitted signal x(t) and the channel response impulse h(t) plus the noise z(t) as in the following equation. 
y(t) = h(t) * x(t) + z(t)
In the frequency domain, the convolution in the time domain can be replaced by multiplication, so that the equation becomes 
Y(n) = H(n) . X(n) + Z(n)
Example of Communication Channels:
- Communication systems convert information into a format into a format appropriate for the transmission medium, some channel convery electromagnetic waves.
- Analog communication systems convert (modulate) analog signals into modulated (analog) signals – amplification to extend distance – noise grows linearly.
- Digital communication systems convert information in the form of bits into binary/digital signals – bit regeneration to extend distance – BER grows, but slowly.


## Channel Modelling
A channel model is a mathematical representation of the effects of a communication channel through which wireless signals are propagated. The channel model can represent the power loss incurred by the signal as it travels through the wireless medium. Channel modelling can be done using Octave. Simple Octave simulation model is provided for plotting the probability density of z and θ.

## AWGN Noise Model (Additive White Gaussian Noise)
The AWGN channel is a well-known model to indicate line of sight (LOS) conditions. This channel model is used to evaluate the difference between a LOS model and a channel model including fast-fading effects. There are types of noise, such as thermal noise, distortions, and external interference. Thermal noise is often modelled as Additive White Gaussian. The performance of a digital communication system is quantified by the probability of bit detection errors in the presence of thermal noise. In the context of wireless communications, the main source of thermal noise is addition of random signals arising from the vibration of atoms in the receiver electronics.


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# Comment
RF engineering is incorporated into almost anything that transmits or receives radio waves across the RF spectrum (3 KHz to 300 GHz), including cell phones, radio and Wi-Fi and any frequency band transmitted is inevitably affected by noise.

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