Floating relay stations enable connectivity in quake-hit areas

It has been more than a month since the magnitude 6.5 and 7.3 earthquakes hit Kumamoto Prefecture, on the island of Kyushu in southwest Japan.

About five years ago, when a massive temblor struck Japan’s northeastern Tohoku region, it took about one and a half months to recover the mobile communications network — a critical lifeline in the modern world. This time, it took about two weeks, thanks to SoftBank’s balloon-based wireless relay system.

Mobile towers

On May 12, the Japanese telecommunications giant launched a white balloon, inflated with helium, in the Taiki area of Hokkaido, the country’s northernmost prefecture. About 10 minutes later, the balloon reached a height of 100 meters. SoftBank tested its base station held aloft by the balloon, aiming to expand coverage areas of the mobile communications network.

The station is capable of receiving radio waves from smartphones, and in this experiment, it transmitted waves to a base station 1.3km away. The phone had a data communication speed of 70 Mbps.

To transmit and receive radio waves at greater heights, wireless relays systems are often placed on iron towers or on the rooftops of buildings. However, the network could be dealt a fatal blow if these towers are damaged. In addition, it takes about three months to fully recover a system that has been extensively damaged, such as in an earthquake.

A balloon-based station can be launched within two hours of arrival on-site. It can receive radio waves from surviving base stations in surrounding but undamaged areas, which then expands cellular coverage. The wireless relay system, which is mounted inside the balloons, weighs about 2.5kg, and can be carried by hand in case roads and transportation systems are limited.

SoftBank thus learned a lesson from the 2011 earthquake and began deploying balloon-based stations across Japan in 2013.

The company sent one into the air in Fukuoka Prefecture, just north of Kumamoto, on April 17. The floating base station provided better connectivity to mobile phones on roads that were important for carrying relief supplies. “We could restore our network faster [than other carriers],” said SoftBank Group Chairman and CEO Masayoshi Son.

Existing models of emergency relay stations are equipped with a 10-meter tall antenna, which only covers an area with a radius of just 1 to 2km.

Balloon-based systems can reach a height of 100 meters and are capable of covering a maximum 10km radius. Obstacles, such as buildings and forests, are less likely to block network traffic. “You can access the network from wherever you can see the balloon,” said Teruya Fujii, a fellow at SoftBank’s research and development division.

Within the coverage area, up to 400 simultaneous phone calls can be made. If the average call is 3 minutes, a total of 8,000 people can make a call within one hour. SoftBank’s latest model also supports its high-speed LTE wireless service, with a maximum communication speed of 150Mbps. Once lifted off the ground, the system can keep operating for up to six months.

The relay system is powered by high-capacity storage batteries and electricity produced by solar panels. SoftBank’s Fujii said the company can set up an on-the-spot relay system even in areas where there is a power outage.

Fujii came up with the idea of using balloons, but they were seen as vulnerable to strong winds, which interrupt communication with other base stations. So, SoftBank redesigned the balloons and made them wider, in the shape of an ellipse. SoftBank also attached the balloons to a so-called scoop, a wing that catches wind and achieves better stability.

In April, the company changed the frequency used for testing the communication between a balloon-moored relay system and a nearby base station from 3.3GHz to 1.5GHz. The move came in line with a government policy update in March, which green-lighted tethered balloons to be used as base stations and radio relay systems. A lower frequency allows for stable connectivity, even in heavy rain. With this change, SoftBank was able to expand its coverage area from a 5km radius to 10km.

SoftBank now deploys 10 balloons at 10 domestic sites, including Hokkaido and Okinawa, Japan’s southernmost prefecture. The company plans to use the balloons for other purposes as well, such as rescue missions in the mountains where people lost in areas outside of service could use their phones to call for help. It could also be deployed at outdoor concert venues, where many people use their phones simultaneously.

One obstacle to full deployment, however, is cost. Helium has a price tag of 130,000 yen ($1,180) per balloon. With on-site operations necessary, there are transportation and labor costs, too. Monitoring and controlling capabilities can be done through the internet.

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