This article explains how modulation methods in wireless communication technology have evolved and how they have influenced the performance of modern communication devices such as smartphones. It highlights the positive impact that the introduction of modern technologies such as LTE has had on our daily lives by enabling high-speed data transfer and reliable communication.
Cell phones first appeared in 1981 using analog communications. At that time, cell phones were simply devices for making voice calls and were quite large in size and weight. With the commercialization of 2G communications in 1991, which is a digital conversion of analog communications, the performance and ease of use of cell phones improved dramatically. 2G communications used digital signals to provide the ability to send and receive text messages in addition to voice calls, and it also provided increased security. In the 2000s, third-generation communications were commercialized, allowing cell phones to send and receive large amounts of data. The cell phones of this era were no longer just calling devices, but the precursors to smartphones with internet access and multimedia capabilities.
By 2011, LTE (long-term evolution), the long-term evolution of 3G, had entered the commercialization phase. LTE enabled high-speed data transfer, making streaming services and large file transfers seamless. This greatly improved the experience for smartphone users and exploded the reach of the mobile internet. Let’s take a look at the research behind this rapidly evolving technology.
Wireless communication technology is basically aimed at transmitting certain information to another party at a distance. In order to do this, when multiple devices send and receive signals at the same time, only the signal emitted by a specific device is accepted, and in wireless communication, the signal is modified by a process called modulation. Modulation does two things: it increases the frequency of the signal and it encrypts the signal. The development of these modulation techniques is at the core of modern wireless communication.
As a simple example, let’s say there are only three cell phones in the world, A, B, and C, and we want to make a call to A. The human audible frequency is in the range of 20 to 20,000 Hz, so the data we send back and forth would be a voice signal with a frequency of 20 to 20,000 Hz. However, if A, B, and C send signals simultaneously without modulation, the signals in the same frequency range will interfere with each other, making it impossible to distinguish A’s signal from the other three. To solve this problem, frequency shifting is used in the modulation process, for example, by increasing the overall frequency by 100 kHz, increasing the frequency of A’s signal by 20 kHz, and increasing the frequency of B’s signal by 40 kHz before transmitting it. The signal from 100 to 120 kHz would then belong to C, the signal from 120 to 140 kHz would belong to A, and the signal from 140 to 160 kHz would belong to B, making it possible to distinguish which signal came from which device. In real-world communications, a frequency around 2 GHz is used to raise the overall frequency. This frequency is called the carrier frequency, and the range of frequencies used by each device is called the bandwidth. In the example above, the bandwidth would be 20 kHz.
On the other hand, if the voice signal is transmitted by increasing the frequency alone, the signal is distorted due to interference from electromagnetic waves in space, which is called noise. In the case of simply increasing the frequency, the amplitude of the electromagnetic wave contains the information to be transmitted, so it is called AM (Amplitude Modulation). However, AM is not used much in real life. The reason for this is that the strength of the signal is relatively weak compared to the strength of the noise, so the original transmitted signal is greatly distorted by the noise compared to other modulation methods. To solve this problem, wireless communication involves encrypting the signal before transmitting it and decrypting it again at the receiver, which varies depending on the modulation method used. The most important aspects of the encryption process are the reliability of the modulation process and the bandwidth efficiency.
The reliability of the modulation process is a measure of how closely the received signal can be interpreted to the original signal when the information originally intended to be transmitted is distorted by noise. A simple example of how to increase reliability is to send a signal multiple times. For example, if you send digital information 1 five times per bit, you’re sending 11111, so even if noise distorts the signal to 11011, it’s easy to infer that the original signal was 1.
On the other hand, when multiple devices interact at the same time, as mentioned earlier, the range of frequencies used by the devices must be different, and the smaller the range of frequencies used by each device, the more devices can communicate in the same range of frequencies. This is called bandwidth efficiency. In the example above, since we’re sending the same information five times, we’d have to send it five times faster to deliver it at the same speed. As a result, the frequency of the transmitted signal would have to be five times higher to send five times as much information, so the bandwidth would be very inefficient in this case. In general, more reliable modulation methods tend to be less bandwidth efficient.
A prime example of the introduction of new modulation methods is LTE. LTE is a standard for high-speed wireless data communications that combines GSM/EDGE and UMTS/HSPA technologies with new modulation methods to increase channel capacity and communication speeds. GSM/EDGE is the 2G communication technology we’re familiar with, and UMTS/HSPA is the name for 3G technology, so LTE is simply a new modulation method for 3G technology that increases the speed. Strictly speaking, LTE is not 4G, as it is often advertised by carriers, but it is a technology that has advantages such as faster speeds, higher throughput, and lower operating costs compared to the existing 3G technology. The history of wireless communication technology shows that the key to advancing wireless communication technology is the development of modulation methods. Even today, researchers studying wireless communications are thinking about how to develop faster and more accurate wireless communication technologies by compensating for the shortcomings of existing modulation methods, and these efforts are gradually bearing fruit in our daily lives.
