1. Why Radio Signals Interfere When Their Frequencies Overlap
If everyone in a classroom speaks loudly at the same time, no one can hear a clear voice. A similar problem occurs with radio waves. When multiple stations transmit on the same frequency in the same location, they interfere with each other, disrupting communication. This is called interference. Because radio waves are a limited resource, countries create rules like licensing systems to organize their use, much like traffic lights manage cars on a road [2]. However, since radio waves are not sound itself, this comparison only helps explain the idea of separating them so they do not overlap.
2. How the Radio Act Aims for Fair and Efficient Use of Radio Waves
The Radio Act sets rules for the use of radio waves. Its Article 1 states that the purpose is to use radio waves "fairly and efficiently" to increase public welfare [1]. "Fairly" means that no single person or group monopolizes the waves. "Efficiently" means using the limited waves without waste. Understanding these two concepts helps explain the next step: the allocation of frequencies.
3. How the Frequency Allocation Plan Divides Up Radio Waves
Based on Article 26 of the Radio Act, the Minister for Internal Affairs and Communications creates and publishes a "Frequency Allocation Plan." This is a table that assigns specific frequencies to different uses, such as broadcasting, mobile communication, and public services [3]. This table helps with applications for radio station licenses and other procedures. You can think of it like a city planning map that designates which areas are for farmland and which are for housing.
4. Why Wi-Fi and Bluetooth Need No License but Still Have Rules
Usually, a license is required to operate a radio station. However, the Ministry of Internal Affairs and Communications lists examples of "radio stations that do not require a license," such as cordless phones, hearing aids, wireless microphones, and Wi-Fi (wireless LAN) [4]. Bluetooth also uses the same 2.4 GHz band. A license is not needed if the device meets specific conditions regarding output power and type. For small-power data communication systems, one condition is that the device has received a "Technical Conformity Certificate" [5]. The usable frequencies and purposes are fixed for each device type to reduce the risk of interference. "No license required" does not mean "do whatever you want."
5. How Low and High Frequencies Differ in Distance and Data
Radio waves with lower frequencies travel along the ground and can bend around mountains and buildings, so they reach far distances. Like AM radio waves, they can sometimes travel quite far depending on conditions. However, with current frequency allocations, it is difficult to secure the wide bandwidth needed for high-speed communication, so the amount of information they can carry at once tends to be smaller [6][8]. Radio waves with higher frequencies behave more like light, traveling in straight lines. They are less likely to reach behind obstacles and have a shorter range, but it is easier to secure wide bandwidth, making them suitable for large-volume communication. Mobile phones often use frequencies around 2 GHz, with a wavelength of about 15 cm (about 6 inches), allowing antennas to fit inside the device body [7][9]. It is rare for one frequency band to provide both long range and high data capacity. Each band has uses it is good for and uses it is not.
6. Why Mobile Phone Companies Want the 700-900 MHz "Platinum Band"
Frequencies in the 700-900 MHz range are often called the "Platinum Band" and are popular with mobile phone operators. This is because radio waves in this band reach easily into buildings and underground areas with many obstacles, and they can cover wide areas [10]. The property that lower frequencies bend around obstacles, seen in the previous section, is valuable here. On October 23, 2023, the Ministry of Internal Affairs and Communications allocated part of the 700 MHz band to Rakuten Mobile. Mobile phones use 715–718 MHz, and base stations use 770–773 MHz, with a width of 3 MHz each [10].
7. How Mobile Phone Frequencies Are Assigned: From Review to Auction
For a long time, frequencies for mobile phones were assigned through a "comprehensive evaluation method." This reviewed the bid price (the amount offered for the frequencies) along with the technical and service content provided by the operator. The price was just one item in the review, not the only deciding factor [11]. A revised Radio Act promulgated on April 25, 2025, introduced a new "radio wave auction" that assigns frequencies to the operator offering the highest price. For now, this applies to higher frequency bands like 26 GHz and 40 GHz [12]. Not all frequencies are subject to auctions. The first auction for the 26 GHz band took place in June 2026. NTT Docomo won the national slot for about 6.29 billion yen, while JTOWER and High-Tech Inter won the regional slots. Results were reported around June 30 [14].
8. How the ITU Divides the World into Three Regions for Radio Rules
Radio waves do not stop at national borders. Therefore, the Radio Regulations of the International Telecommunication Union (ITU) divide the world into three regions. They set international allocations for services such as broadcasting, mobile, and satellite. Japan falls into Region 3 [13]. This allocation is reviewed every 3-4 years at the World Radiocommunication Conference (WRC) [13]. When countries consider their own allocations, these global agreements serve as a foundation.
9. Activities to Investigate Radio Waves Yourself
You might try the following activities. Look at your home Wi-Fi router or its manual with an adult and see if you can find numbers like "2.4 GHz" or "5 GHz." Consider whether the numbers you find are on the "low frequency" or "high frequency" side described in this article. Visit the Ministry of Internal Affairs and Communications website to look at the actual Frequency Allocation Plan table [3].