What happens when the road is narrow, but the cars keep increasing?
Traffic jam.
The world of mobile radio was facing the same thing.
“Which company are we talking about?” you wonder. SoftBank.
SoftBank marked 20 years since entering the mobile phone business on October 1, 2026, and held a briefing for the press. Keitai Watch reported on it (October 2, 2026).
In this article, I keep the reported facts and the background radio knowledge separate.
The 30-second version
- When SoftBank bought Vodafone, all it held was 60 MHz in total: the 1.5 GHz and 2.1 GHz bands. It had no platinum band (700-900 MHz), which bends around obstacles more easily
- The 900 MHz platinum band was allocated to it in March 2012
- Today, it is working on building AI into base station control (AI-RAN) and running trials with 6G in mind
First, frequency is “the width and type of the road”
Frequency is the road that radio waves travel on.
Roads come in two kinds.
- Low frequency: Bends around obstacles easily and reaches inside buildings. But it can carry only a limited amount of data at a time
- High frequency: Can carry a lot of data. But it is weak against walls and obstacles, and doesn’t travel far
The platinum band is the classic example of the former. Why it connects even inside buildings is explained with a drum and violin analogy in the platinum band article.
In other words, a company without the platinum band started competing without a road that reaches beyond walls.
What was reported (facts)
The speaker at the briefing was Tetsuya Nagano, head of the Mobile Network Division. According to the reports, this is what was said.
- At the time of the Vodafone acquisition, the allocation was only 60 MHz in total, in the 1.5 GHz and 2.1 GHz bands
- Getting the platinum band was something they “wanted at all costs” (paraphrased)
- In March 2010, they announced a “Radio Wave Improvement Declaration.” The plan was to double base stations from 60,000 as of 2010 to 120,000 the following year
- They added free Wi-Fi spots to spread the load off the mobile network
- The 900 MHz platinum band was allocated in March 2012, six years after the Vodafone acquisition (2006)
- Nine months after service launched in July 2012, they had deployed 20,000 stations, above the 16,000 they had applied for
It was also explained that the platinum band alone couldn’t handle ever-growing traffic. So they built out LTE in parallel.
Two ways to handle “not enough road”
This section is my own organization, based on the reports.
1. Add more roads Add base stations. Add usable frequencies. Combine two frequencies (carrier aggregation).
2. Use the roads more cleverly Control base stations in coordination to cut interference between frequencies. SoftBank is reported to have moved from the 4G era to C-RAN, which controls multiple base stations together, and to have kept interference down.
If you can’t add roads, make the traffic lights smarter. That’s the idea.
What is AI-RAN? (As far as the article says)
At the briefing, using AI to control base stations was described as the next axis of evolution.
- Until now, base stations controlled radio using rules set in advance
- The aim is to put a mode in which AI runs inference inside those base stations, and optimize radio in real time according to congestion
- Behind this is the view that as AI devices, robots, and XR spread, demand for uplink will grow in communication that used to be mostly downlink
- To handle uplink, they are advancing things like “HPUE,” which raises the transmit power of devices
- They have also started testing their own large model trained on the communication data they hold and their operational know-how. The idea is to detect warning signs and prevent outages before they happen
Note that the body of the report doesn’t give a formal definition of AI-RAN. Reading it as “an effort to put AI in base stations and make radio control smarter” seems natural within what was reported. That is my own reading.
Connecting this to Rakuten Mobile
From here on, this is my view.
One thing all carriers share is that they are all working within “frequency limits” and “capacity limits.”
Rakuten Mobile has also announced an effort to automatically adjust antenna tilt with AI. As I wrote in the physical AI article, the move to build AI into base stations doesn’t seem to be just SoftBank’s story.
I also cover efforts to build temporary base stations from the sky for disaster response in the drone base station article.
What users should look at is not the company name but whether it actually connects where you live your life. I’ve summarized the changes to Rakuten Mobile’s roaming in another article.
Summary
- SoftBank started competing without the platinum band, and it is reported that the allocation came in March 2012
- Frequency is like a road. Low frequencies bend around walls easily, and high frequencies carry a lot
- When you can’t add roads, make base station control smarter. AI-RAN is an extension of that
- Building AI into base stations has started at other companies too. The deciding factor is whether it connects where you live
Source: Keitai Watch
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