How Wireless Communication Works
Have you ever wondered how text messages, pictures, and videos are sent to your wireless phone? Every day billions of devices around the world connect and share data at the speed of light. It may look like magic, but it’s really just a powerful, invisible, and under-appreciated force known as electromagnetism.
Electromagnetism is one of the four fundamental forces in nature. As the name suggests it is the interaction between the electric and magnetic fields. Electricity and magnetism were originally thought to be separate forces, but were unified when James Clerk Maxwell published his Treatise on Electricity and Magnetism in 1873 showing that both phenomena could be explained by one force. In this article, we explore how this force is used in all forms of wireless communication.
Electromagnetic Waves
An electromagnetic wave is a disturbance in the electromagnetic field. This field exists everywhere, and disturbances in this field exist around the presence of electricity or magnetism. If the electromagnetic field is like water in a lake then electromagnetic waves are like ripples in the water.
How Waves Are Transmitted
An electromagnetic wave is created when there is a disturbance in the electromagnetic field. A disturbance like this can be created when you do something as simple as briefly touch both ends of a wire to the terminals of a battery. This allows an electric current to flow through the wire, which in turn creates a weak electromagnetic wave which expands outward in all directions. The wave created in our example would not travel far and would not contain any information. If it were intercepted by a radio transmitter, it would just sound like static. But this example illustrates the power and simplicity of radio technology and sets the stage for our next topic.
How Waves Carry Information
In the early 20th century radio waves transmitted data as Morse code. This process of information transfer was slow and had limited capabilities. World War I and II dramatically accelerated the development of modern radios, contributing to the first commercial radio broadcasting in the 1920s.
Today electromagnetic waves can represent, and therefore transmit, virtually any kind of data imaginable. Just as waves in a lake move up and down as they expand outward, electromagnetic waves do much the same thing. Note that these kinds of waves resemble a sine function, as seen below.
We can encode information into a standard sine function by modulating (or changing) some property of the function such as amplitude or frequency. This is where we get the names for AM and FM radio: AM radio uses amplitude modulation while FM radio uses frequency modulation. Each wave created propagates through space at the speed of light to be eventually intercepted by an electrical conductor, like an antenna, where the original information can be obtained by decoding the modulated function.
For example, suppose you wanted to send binary digits using this method. You could represent a zero using a standard sine wave and represent a one using a sine wave with an amplitude twice as large. For each period of time each wave could be interpreted as either a zero or a one, allowing you to transmit binary data at the speed of light using standard radio technology.
A limited number of frequencies can be used to send electromagnetic waves, so we designate ranges of frequencies for certain purposes, which collectively make up the radio spectrum. Using different frequencies allows multiple radio signals to be sent at the same time, in the same area, and be distinguishable from one another. When you visit a radio station on 95.1 FM, for example, you are tuning into a radio station that broadcasts at an electromagnetic frequency of 95,100,000 cycles per second. By listening to only this frequency, your radio is able to distinguish this radio station from others.
Sending and Receiving Information
Transmitting information between two devices using radio waves requires a transmitter and a receiver. The transmitter takes information like audio or video, encodes it into a sine function, and transmits the function into the air in the form of an electromagnetic wave. The receiver detects the wave and decodes the data. Antennas are used by transmitters to transmit waves and also by receivers to detect them.
Electromagnetic waves can travel anywhere from a few miles (for television broadcasts) to millions of kilometers (for deep space transmissions) depending on the power of the transmission. As radio waves propagate out into space in every direction they lose a small amount of energy and become harder to detect. Accordingly, higher powered transmitters must be used to send radio waves over a longer distances.
The Force Is All Around You
The ability to sense electromagnetic waves is known as magnetoreception, and is an ability shared by many in the animal kingdom including birds, bats, fruit flies, and mice. Birds are known to use the earth’s magnetic field for navigation — an ability that helps them orient themselves relative to the ground and develop regional maps.
Although we can’t see them, there are countless electromagnetic waves all around us traveling at the speed of light. Electromagnetic waves are used for television broadcasts, cell phones, Bluetooth, radio, and every other form of wireless communication.
