Japan’s four major operators — SoftBank, NTT DoCoMo, au (KDDI), and Rakuten Mobile — expanded their 5G networks ahead of the Expo 2025 Osaka held on Yumeshima Island from April 13 to October 13. From April 13 to June 6, Speedtest Insights data revealed key differences in user experience across networks.
Investments
SoftBank has teamed up with KDDI through their 5G JAPAN JV to jointly build 38,000+ 5G base stations, cutting capex by ¥45 billion each between FY2020–FY2023, and planning up to 100,000 stations per carrier by FY2030, saving ¥120 billion in capex per company, The Wall Street Journal reports.
Meanwhile, SoftBank Group (the holding company) is deploying massive investments globally — notably pledging $100 billion into the U.S. over four years focused on AI infrastructure, and committing around $500 billion over four years into Stargate with OpenAI, contributing $15–25 billion to OpenAI’s funding by early 2025, The Times reports.
NTT DoCoMo’s standalone mobile unit spent ¥714 billion (~$4.9 billion) on capex in FY2024 — with plan to boost this by 23 percent in 2025 to support accelerated 5G deployment, raising urban base station count by ~20 percent, Lightreading reports.
DoCoMo is investing ¥233.6 billion to acquire a 66 percent stake in SBI Sumishin Net Bank as part of a ¥739 billion (~$5.1 billion) deal. The NTT Group reports capital investments of ¥2.13 trillion in FY2025.
KDDI aligned with SoftBank on the JV, saving ¥45 billion capex FY2020–FY2023, with plans for ¥120 billion capex savings by FY2030, Mobile World Live reports. KDDI has indicated its heavy 5G investment has peaked, freeing capital for diversification into AI and data‑center businesses.
Rakuten Mobile, after spending ¥168 billion in 2023 and ¥81 billion in 2024 on network build‑out, plans to increase capex again to ¥150 billion in 2025 to support its growth trajectory, Telecom TV reports.
Since launch, Rakuten has invested a cumulative ¥1.8 trillion (~$11.8 billion) to build its cloud‑native mobile infrastructure. There was also a ¥300 billion reduction in expected capex over 2023–2025 related to a low‑band roaming deal with KDDI.
Coverage and Signal Strength
SoftBank and NTT DoCoMo provided the most consistent 5G coverage, with average signal strengths (RSRP) of –83.52 dBm and –83.74 dBm, respectively. This translated to better connectivity across indoor and high-traffic areas.
Rakuten Mobile and au lagged in coverage, with weaker signals (–92.62 dBm and –93.60 dBm), suggesting patchy reception or limited base station reach in certain zones. Despite these disparities, signal quality (RSRQ) remained within a “good” range across all carriers, between –12.58 dB and –13.01 dB, indicating stable performance under load.
Speed and Consistency
au delivered the fastest and most consistent 5G speeds, with a median download speed of 384.68 Mbps, followed by DoCoMo at 320.07 Mbps. SoftBank and Rakuten trailed at 270.98 Mbps and 200.96 Mbps, respectively. Notably, au’s lower-tier users (10th percentile) also experienced strong performance, showcasing solid network optimization.
Upload speeds told a slightly different story — SoftBank led at 37.45 Mbps, closely followed by au at 36.36 Mbps. DoCoMo and Rakuten delivered lower upload performance, at 21.78 Mbps and 18.43 Mbps, respectively.
Public Wi-Fi vs 5G
On the Expo’s opening day, public Wi-Fi access was limited and unstable, prompting quick intervention by organizers to expand bandwidth and coverage. Despite improvements, Wi-Fi performance remained modest, with a download speed of 66.94 Mbps — adequate for light usage but far below the 5G median of 305.63 Mbps. Interestingly, public Wi-Fi outperformed mobile 5G in upload speeds, recording 43.82 Mbps vs 29.74 Mbps, possibly benefiting from lighter uplink usage.
Stability and Network Load Management
Initial connectivity issues underscored the challenges of managing real-time demand at large-scale events. Yet, by mid-April, carriers had stabilized their networks through signal boosters and additional 5G base stations. Among them, SoftBank, DoCoMo, and au demonstrated strong resilience, maintaining high throughput and reliability throughout the event window.
Baburajan Kizhakedath
