This article covers the role of frequencies and their importance in communications technology. It explains the concept of frequency and its impact on communications, discussing how it is used, especially in wireless communications, and how to efficiently manage the limited frequency resource.
Humans have long sought to overcome temporal and spatial limitations to communicate information. Storing information on media such as CDs and tapes overcomes temporal limitations, and radio broadcasts, which are often listened to in cars, are an example of information delivery overcoming spatial limitations. We call this telecommunications, and the breakthroughs in modern wireless communications are largely due to the study of the frequency domain. The dictionary definition of frequency is “the number of cycles of a wave in which the same state is repeated within a given time,” but in engineering it means much more than that. Understanding frequency requires a mathematical and physical background, but in this article, we’ll try to explain it in as simple and intuitive a way as possible to illustrate its power and importance in modern society.
We are naturally familiar with the realm of time. Consider a situation where you’re at a concert and you’re shouting a message to a friend 100 meters away: you’re the transmitter of the information, your friend is the receiver, and the message you’re conveying is a piece of information. Other sounds occurring at the same time, such as the singer singing or the crowd cheering, are not important to your friend and can be considered noise. This is where the problem of communication in the time domain comes in. When multiple pieces of information exist at the same time, they can interfere with each other and cancel out the desired information. Just as the sound at a concert is too loud for your friend to hear your message, it’s difficult to get the information you want if the receiver is heavily influenced by noise. This problem is exacerbated by the fact that the longer the communication distance increases, the weaker the signal becomes, which increases the relative strength of the noise.
To overcome this problem, scientists have applied the method of sending information in the frequency domain, which provides a new perspective by considering frequency as a variable instead of time as a variable. When a sender sends information that makes sense in the frequency domain, the receiver can filter out signals at other frequencies if it knows the promised frequency. In the simplest example, the human ear can be viewed as a filter. For example, humans cannot perceive sounds outside the audible frequency range of 16 Hz to 20 kHz, such as ultrasonic waves from dolphins. So how do we make a signal meaningful in the frequency domain? In the case of radio broadcasts, we can think of it as carrying information in a sinusoidal wave with a promised frequency. AM varies its amplitude according to the information, while FM uses frequency changes to convey information. This is why, even if stations are broadcasting at the same time, the receiver can tune in to hear only the desired broadcast. Signals converted to the frequency domain are free from interference in the time domain.
However, the same problem can occur in the frequency domain. If multiple pieces of information are transmitted on the same frequency, they can interfere with each other, making it difficult for the recipient to receive the desired information. However, if each frequency is assigned to a specific user, the problem is different. Everyone has the same amount of time. In modern communications, speed is of the essence, and it’s obvious to decide whether to allocate time to send information every second or minute, or to allocate frequencies to send information at the same time. Frequency-based communication is used in radio, TV, cell phones, and more.
But as always in engineering, there are trade-offs. Starting with simple information, more frequency bands are needed to transmit higher quality signals like voice or video. So everyone wants to use more frequency bands. The solution is either to have an infinite number of frequencies available, or to allocate the limited frequencies equitably. However, due to technical limitations, there is a finite amount of spectrum available, and spectrum is a resource. The astronomical amounts of money that are bid on in national telecom spectrum auctions demonstrate the importance of spectrum. Even in the U.S., essential resources like gas and electricity are privately managed, but spectrum is directly controlled by the state. This means that the importance of spectrum needs no introduction.
People who are worried about paying a lot for calls might think that they could theoretically steal spectrum and make calls for free. However, it’s probably best not to try this. You never know when people in black suits will come knocking on your door accusing you of unauthorized use of spectrum.
