In this blog post, we’ll take an easy-to-understand look at how radio wave frequency and wavelength influence the speed and quality of mobile communications, and why ultra-high-frequency waves are central to modern communication networks.
Since the advent of smartphones, mobile wireless communication has become an indispensable part of modern life. Although the radio waves used in mobile wireless communication are invisible and difficult to perceive, they are a type of electromagnetic wave, just like visible light and X-rays. Radio waves travel through the atmosphere at approximately 300,000 km per second, which is exactly the same as the speed of light in a vacuum. Generally, radio waves refer to electromagnetic waves that oscillate between approximately 3,000 and 3 trillion times per second. The number of oscillations per second is called the “frequency,” and one oscillation per second is defined as 1 Hz. Therefore, radio waves have frequencies ranging from 3 kHz to 3 THz. Furthermore, frequency is inversely proportional to “wavelength,” which refers to the length of a single wave; the higher the frequency, the shorter the wavelength, and the lower the frequency, the longer the wavelength. The product of the frequency and wavelength of an electromagnetic wave is constant and equals the speed of light.
The reason mobile wireless communications use radio waves in a lower frequency band than visible light or X-rays is that they facilitate the transmission of information over long distances. As frequency increases, electromagnetic waves become more directional and are more easily absorbed or scattered by dust or water vapor in the atmosphere, resulting in signal attenuation. Conversely, radio waves with lower frequencies have excellent diffraction and penetration properties; they bend around obstacles and can pass through thin walls to propagate over long distances. Among radio waves in the 3 kHz to 3 GHz band, very long waves (VLF) and long waves (LW) with frequencies of 0.3 MHz or lower can travel extremely long distances and are primarily used for public purposes such as maritime communications, beacon communications, and the guidance of ships and aircraft. Frequencies in the 0.3–800 MHz band are utilized for shortwave broadcasting, international broadcasting, FM radio, and terrestrial analog TV broadcasting. Ultra-high-frequency (UHF) waves in the 800 MHz to 3 GHz band are primarily used for mobile wireless communications and are divided into four main bands: the “800–900 MHz band,” the “1.8 GHz band,” the “2.1 GHz band,” and the “2.3 GHz band.” Since the advent of the smartphone era, the importance of efficient frequency management in the VHF band has grown significantly, and since the advent of 5G, the use of higher frequency bands (ranging from several GHz to tens of GHz) has been expanding technologically. Meanwhile, radio waves in the 3 GHz and higher bands have very strong directionality and are primarily used in special situations where there are no obstacles in the path, such as satellite communications or space communications.
The reason ultra-high frequency bands are used in mobile wireless communications is that they can transmit more information in a shorter time than the 0.3–800 MHz band. For example, assuming that four waves are required to transmit 1 bit of data, an ultra-low frequency signal of 1 kHz generates 1,000 waves per second, allowing only 250 bits of information to be transmitted per second.
However, an 800 MHz UHF signal generates 800 million waves per second, allowing it to transmit 200 million bits of information per second, while a 1.8 GHz UHF signal can process a massive amount of information equivalent to 450 million bits per second. To compensate for the limited long-distance transmission capabilities of these ultra-high-frequency waves, mobile wireless communication systems install wireless base stations as densely as possible within a narrow area of about 2 to 5 km in radius to transmit and receive radio waves. These base stations are then connected via wired links to transmit information via a relay system, thereby minimizing dead zones. Similar to mobile wireless communications, terrestrial digital TV broadcasting using UHF also strives to erect transmission towers at the highest possible locations to reduce obstacles along the radio wave path.
The use of UHF has also dramatically improved the portability of mobile communication devices. The effective length of an antenna required for efficient reception is approximately 0.25 to 0.5 times the wavelength of the received signal; however, by utilizing high-frequency bands such as UHF, highly efficient transmission and reception have become possible even with antennas smaller than the palm of a hand. These technological advancements have enabled the miniaturization and high performance of modern mobile communication devices, including smartphones, and, along with the expanded use of high-frequency bands, are laying the foundation for an even more sophisticated mobile communication environment in the future.
