Japan is famous for its high-speed trains and scenic railway journeys—but if you’re a traveler using an eSIM in Japan, you might wonder: Will my connection hold up inside long tunnels or during high-speed travel?
KDDI-au’s article “トンネルでもスマホの電波がつながる仕組みとは？” dives into the real-world network solutions that make it possible to use your smartphone seamlessly on trains like the Limited Express Azusa—and even on the Shinkansen (bullet trains).
The Challenge: Connectivity Inside Tunnels and at High Speeds
Trains like the Limited Express Azusa, which connects Tokyo and Nagano through mountainous regions, pass through numerous long tunnels. In the past, these areas were notorious for dropped calls and lost data signal.
Similarly, Japan’s Shinkansen trains, traveling at speeds up to 300 km/h, face their own challenges:
- 📶 Maintaining signal stability while rapidly moving between base stations
- 🛤️ Delivering coverage through tunnels and shielded stations
- 🧱 Handling interference from thick concrete and underground environments
KDDI-au’s Solution: Tunnel Antennas and Intelligent Infrastructure
KDDI-au engineers have implemented a robust system of:
- 📡 Leaky coaxial cables and dedicated antennas installed along tunnel walls
- 🔁 Signal repeaters to relay 4G LTE and 5G coverage within tunnels
- 🚄 Speed-adaptive systems that ensure a stable connection even at high velocity
- 👷♂️ Ongoing field tests (like those done aboard the Azusa train) to monitor and improve performance
These efforts ensure that passengers on the Azusa—and increasingly on other major train lines—experience consistent mobile access, even underground.
Shinkansen Coverage: What to Expect
In addition to the Azusa line, KDDI-au has also expanded mobile coverage on major Shinkansen routes, including:
- 🚅 Tokaido Shinkansen (Tokyo – Kyoto – Osaka)
- 🚅 Hokuriku and Tohoku Shinkansen lines
- 🧳 Station platforms, waiting areas, and even inside cars
Coverage typically includes 4G LTE as a base, with 5G being introduced progressively, especially at major stations and along surface routes.
This means that eSIM users can:
- ✅ Stream music, browse the web, and check maps inside tunnels
- ✅ Use messaging apps or video calls without interruption
- ✅ Stay connected from departure to arrival—even across mountains
What It Means for eSIM Travelers in Japan
For international travelers using eSIMs with unlimited data, this technology ensures:
- 📶 Reliable mobile access across your entire rail journey
- 🗺️ No stress about losing maps or translation tools mid-trip
- 🚄 Confidence in using mobile tickets, hotel confirmations, or e-wallets
- 📱 A truly connected travel experience—even in Japan’s most remote rail corridors
Conclusion
Whether you’re riding the Limited Express Azusa to the Japanese Alps or zooming across the country on the Shinkansen, KDDI-au’s advanced tunnel coverage ensures your eSIM stays connected—every step of the way.
Ready for high-speed travel with uninterrupted mobile access?
👉 Buy your eSIM now and stay connected above ground, underground, and everywhere in between.
