Background Knowledge - Communications Systems

This information is pulled from this document from the google drive. Created by Christopher Arjune on May 29th 2020. 

Radio Frequency

Wireless communication uses electromagnetic radiation to transmit data as opposed to wired connections. This typically involves a transmitter, which converts digital data into analog signals that is sent to a receiver which decodes the analog waves back into digital data to process.

Figure 1. Electromagnetic Spectrum. RF communication generally occurs in the range of 3kHz to 300GHz

High frequency signals can convey more data, however there are tradeoffs for this, mainly being that at higher frequencies signals have reduced propagation through air and non-metallic materials, and are more likely to reflect off metallic objects. With this in mind, the rover currently uses a 900MHz frequency antenna to transmit important status information and commands, while 2.4GHz is being used to transmit video feed. In reality, the 900MHz frequency band actually ranges from 902-928 MHz frequencies, and we can adjust the frequencies as needed.

Terminology

dBm - power ratio in decibels referenced to 1mW x=10log(P/1mW), where P is power

dBi - power ratio in decibels with reference to an isotropic radiator, where signal is equal in all directions from the source (antenna radiation patterns only change the shape of the signal, and don’t increase or decrease total power)

Rule of thumb: double the power = 3dB increase

Basic Components of an RF System

The only major components required are a router and antenna, which will process information and interface with the rest of the software, and then transmit and/or receive information to/from another source. The router is the device that processes all of the data and outputs or receives a signal at a certain power level (dBm). The antenna amplifies received or outputted signal by concentrating it into a more directional spread. At the most basic, signal outputs isotropically, or in a spherical pattern (this is physically impossible). By concentrating the signal into a disc/toroid shape (dipole-ie rubber duck antenna, omnidirectional), the signal becomes stronger where there is signal being concentrated. Even more directional antenna focuses the signal into a conical pattern, such as yagi or parabolic antenna.

Something to consider in the future could be creating our own RF module, which would allow for greater customizability, but would require additional research and design time.