In this blog post, we’ll explore the origin of the term “cellular phone”—which we use every day—and examine why the concept of a “cell” is important by looking at how cellular communication systems work.
One of the most commonly used examples of “Konglish” in South Korea is probably “handphone.” Anyone who has learned a little English would confidently say, “A cell phone isn’t called a ‘hand phone’ in English—it’s a ‘cellular phone’!” Strangely enough, however, a literal translation of “cellular phone” is “cell phone.” Anyone who has found this fact intriguing may have imagined a cell phone made of cells at least once. So what exactly are these “cells”?
These “cells” aren’t the mobile phones themselves, but a concept derived from how mobile phone service is provided. To provide mobile phone service, telecommunications carriers divide the entire service area into small hexagonal zones—called “cells”—that resemble a beehive. When a user makes a call, the base station responsible for the cell where the user is currently located provides the call service. The term “cellular phone” was coined because the arrangement of these cells resembles the clustering of biological cells. So why do telecom operators specifically use this cellular structure? Let’s now examine the reasons for dividing the service area into cells.
Before understanding the mobile phone communication system, let’s first consider how general wireless communication works. General communication is similar to a situation where many people are talking at the same time inside a large room. Even though the surroundings are very noisy, we can distinguish our friend’s voice from those of others and convey our thoughts to our friend using our own voice. This is because humans can effectively distinguish the desired voice from other sounds.
Similarly, communication devices use “frequency bands” and “PN codes (Pseudo-Noise Codes)” to distinguish only the desired signal from among countless others. Each communication device transmits radio waves carrying information within a specific frequency band assigned to it. Even when numerous radio waves are present simultaneously, the receiving device can accurately extract the desired information simply by selecting the frequency band it is supposed to receive. In other words, by using different frequency bands, multiple communication signals can be distinguished from one another. Furthermore, even when using the same frequency band, if each device is assigned a unique PN code—which acts as a kind of cipher—multiple users can communicate simultaneously within that same frequency band. This method was most notably utilized in CDMA (Code Division Multiple Access) technology.
Let’s return to the topic of cell phones. To communicate via a cell phone, a device is needed to connect the signal regardless of the user’s location, and base stations fulfill this role. If a base station were installed in only one location, communication would be possible in the immediate vicinity but impossible in more distant areas. Therefore, multiple base stations must be installed at regular intervals to ensure communication is possible anywhere. Meanwhile, base stations operated by the same telecommunications carrier share the same frequency resources, but each base station manages communications by assigning unique identification information to the users communicating through it.
This raises a major problem. Consider a user located between two adjacent base stations, A and B. Suppose this user is communicating using a specific PN code assigned by base station A; at the same time, base station B might coincidentally assign the exact same PN code to another user. In this case, if both signals reach the user simultaneously, it becomes difficult to accurately distinguish the intended signal. This phenomenon is called interference. If the distance between base stations is increased excessively to avoid interference, areas where communication becomes impossible will arise; therefore, a new method was needed to ensure communication is possible everywhere while minimizing interference.
The concept of a “cell” was introduced to solve this problem. As explained earlier, cells are arranged in a hexagonal pattern, like a beehive, to completely cover the entire service area without gaps. Telecommunications providers assign different numbers to each cell, ensuring that adjacent cells are not assigned the same number. They then divide the total available frequency resources into several groups, with each cell using only the frequency group assigned to it. Thanks to this “frequency reuse” technique, communication services can be provided efficiently even over a wide area while significantly reducing interference.
First, let’s assume that the base stations responsible for each cell are installed at appropriate intervals to ensure stable communication throughout the entire area. A user located between two adjacent base stations can receive signals from both stations simultaneously. Even if the same PN code is used, since the two base stations operate on different frequency bands, the user can accurately receive the desired signal simply by selecting the frequency of the base station they are currently using. Furthermore, since cells using the same frequency band are spaced far enough apart, the likelihood of mutual interference is greatly reduced.
What happens if a user moves from Cell A to the adjacent Cell B while on a call? As the user moves, the signal from Base Station A gradually weakens, while the signal from Base Station B grows stronger. The network detects this change and switches the connection to Base Station B at the appropriate moment, assigning new wireless resources. Since this process occurs in a very short amount of time, the user hardly notices any interruption in the call. This process is called a “handover.”
It is precisely thanks to this ingenious communication technology that today’s cellular phones were made possible. From now on, when you hear the term “cellular phone,” rather than picturing a strange mobile phone made of cells, you will first think of the technology that organically connects countless cells and base stations to enable stable communication anytime, anywhere. It is thanks to this cell-based communication technology that we can naturally converse with our loved ones on our mobile phones.
