In this blog post, we will examine why signals can be transmitted accurately despite noise in wireless communications through modulation methods, reliability, and bandwidth concepts.
Analog mobile phones first appeared in 1981. At that time, mobile phones were simply devices for voice calls, and they were quite large and heavy. Then, in 1991, 2G communications, which converted the existing analog communication system to digital, became commercially available, greatly improving the performance and usability of mobile phones. 2G communication used digital signals to provide voice calls and text messaging, and security was also enhanced. In the 2000s, third-generation communication became commercially available, enabling mobile phones to send and receive large amounts of data. Mobile phones that appeared at this time went beyond simple communication devices and became the beginning of smartphones with Internet access and multimedia capabilities.
In 2011, LTE (long-term evolution), which represents the long-term evolution of 3G, entered the commercialization stage. LTE enabled high-speed data transmission, allowing for smooth streaming services and large file transfers. This greatly improved the user experience for smartphone users and led to an explosive increase in the use of mobile internet. Let’s take a look at the research on wireless communication technology, which is developing at such a rapid pace.
Wireless communication technology is basically aimed at transmitting specific information to a remote location. When multiple devices send and receive signals simultaneously, wireless communication undergoes a process of signal transformation, called modulation, in which only the signals emitted from a specific device are received. Modulation has two functions: increasing the frequency of signals and encrypting signals. The development of modulation technology is the core of modern wireless communication.
As a simple example, suppose that there are only three cell phones, A, B, and C, in the world, and we want to call A. The human audible frequency range is 20 to 20,000 Hz, so the data we send and receive will be voice signals with frequencies between 20 and 20,000 Hz. However, if A, B, and C send signals simultaneously without undergoing modulation, interference will occur between signals with the same frequency range, making it impossible to distinguish the signal from A among the three signals. To solve this problem, frequency shifting is performed during the modulation process. For example, the overall frequency can be increased by 100 kHz, the frequency of signal A can be increased by 20 kHz, and the frequency of signal B can be increased by 40 kHz before transmission. Then, the signal between 100 and 120 kHz is C, the signal between 120 and 140 kHz is A, and the signal between 140 and 160 kHz is B, making it possible to distinguish which signal came from which device. In actual communication, the frequency is raised by about 2 GHz overall. This frequency is called the carrier frequency, and the range of frequencies used by each device is called the bandwidth. In the above example, the bandwidth is 20 kHz.
On the other hand, when voice signals are transmitted by raising only the frequency, interference from electromagnetic waves in the space causes signal distortion. The electromagnetic waves in the space are called noise. In the case of transmission by simply raising the frequency, the information to be transmitted is contained in the amplitude of the electromagnetic waves, so this is called AM (Amplitude Modulation). However, AM is not widely used in everyday life. This is because when AM is used, the signal strength is relatively weak compared to other modulation methods, and the original transmitted signal is greatly distorted by noise. To solve this problem, a type of encryption process is applied to the signal before transmission, and the signal is then decrypted by the receiver. This process varies depending on the modulation method used. The most important factors in the encryption process are the reliability of the modulation process and the efficiency of the bandwidth.
The reliability of the modulation process is a measure of how closely the received signal can be interpreted as the original signal when the information originally intended to be transmitted is distorted by noise. A simple example of a method for increasing reliability is to send the signal multiple times. For example, when transmitting digital information 1, if you send it five times per bit, you will transmit 11111, so even if noise distorts the signal to 11011, you can easily infer that the original signal was 1.
On the other hand, as mentioned earlier, when multiple devices interact simultaneously, the frequency ranges used between devices must be different. In this case, the smaller the frequency range used per device, the more devices can communicate with the same frequency range. This is called bandwidth efficiency. In the example above, since the same information is sent five times, the information must be sent five times faster in order to transmit the information at the same speed. As a result, in order to send the information five times, the frequency of the transmitted signal must be five times greater, so in this case, the bandwidth efficiency is very low. In general, the more reliable the modulation method, the lower the bandwidth efficiency tends to be.
A representative example of the introduction of a new modulation method is LTE. LTE is a standard for high-speed wireless data communication, which means that channel capacity and communication speed have been increased by using new modulation methods for GSM/EDGE and UMTS/HSPA technologies. GSM/EDGE is the 2G communication technology we are familiar with, and UMTS/HSPA is the name of 3G technology. In short, LTE is a new modulation method for 3G technology that increases speed. Strictly speaking, LTE cannot be called 4G as it is often advertised by mobile carriers, but it still has advantages over existing 3G technology, such as faster speed, higher throughput, and lower operating costs. As you can see, the history of communication technology shows that the key to the advancement of wireless communication technology lies in the development of modulation methods. Today, researchers in the field of wireless communication are still trying to figure out how to overcome the shortcomings of existing modulation methods and develop faster and more accurate wireless communication technologies, and their efforts are gradually bearing fruit in our daily lives.
