Satellite communication even on a bumpy ride
Having an Internet connection on a plane or on board a ship is undoubtedly useful. A more fundamental role for satellite communication, however, concerns extreme events like tsunamis and earthquakes. Telephone lines and cellular networks are often no use to rescue teams after these kinds of natural disasters, as the lines are generally dead. Communication via satellite is therefore the only option left. However, this is also not without problems. If the links are overloaded, the connection fails – and this can happen even during a simple storm. It also takes time for the rescue teams to set up the necessary small satellite stations in among all the destruction. Another shortcoming is that the receiver must not make any fast movements. Instead, the satellite antenna has to be pointing directly at the satellite (as is the case with TVs). While the steady movement of aircraft and cruise ships means the links work well in those contexts, someone driving a car down a dirt road has almost no chance. Drivers have to stop if they need a connection.
Rescue teams should be able to communicate more easily in future thanks to the KASYMOSA project (Ka-band systems for mobile satellite communications) in which we together with a number of other partners developed an innovative communications system. Among those involved were Technische Universität Ilmenau, Industrieanlagen-Betriebsgesellschaft mbH Ottobrunn IABG, and the German Aerospace Center (DLR). “We’ve basically made satellite communication fit for mobile use,” says project manager Florian Raschke. “Our development eradicates the main disadvantage of satellite communication. The connection is also much more reliable: the bandwidth during transmission is so big that the connection won’t even cut out if it’s overloaded. We’ve also removed the inconvenient and time-consuming task of setting up a transmitting station.”
Let’s start by taking a look at the moving systems, and at how we overcame this shortcoming in satellite communication: When a car drives over potholes and around bends in the road, the antenna corrects its position in a fraction of a second. This happens with a high level of precision, as the antenna only ever moves 0.2 degrees out of the satellite’s focus. To put this in perspective, the car’s antenna would move more than that if a person got into the car. We achieved this using a special mechanical system and, above all, with algorithms that allow us to adjust the antenna precisely and quickly. The antenna itself is also the product of much development work. With diameters of 60 centimeters, conventional satellite dishes are too big to install on the roof of a car. This is why we use a flat satellite antenna, known as a panel antenna. Although panel antennas are already available on the market (they are installed in aircraft, for example), these models cannot withstand being driven over bumpy roads. “So our partners at Technische Universität Ilmenau developed their own flat antenna that meets the requirements very well,” says Raschke.
Another improvement lies in the reliability of the connections. We have modified the data processing so that the data rate changes according to the situation. So if the line is overloaded, the conversation doesn’t cut out entirely, as was previously the case. All that happens is the transmission quality decreases – in the same way as happens with Internet connections. We achieved this with a special modem developed as part of the project that transmits the data. “It enables us to reach very high data rates of several megabits per second,” says Raschke. “Of course, this is nowhere near the gigabit streams of a fixed data line, but it is a major step forward for satellite communications.” This means rescue teams will be able to send maps, and videos of the situation on the ground, secure in the knowledge that the connection will not cut out. They will also be able to make clear satellite calls without any interruptions and without being disconnected.
Rescue teams will also no longer have to set up transmitting stations. “With our system, every terminal – which comprises an antenna and a modem installed in the car – can transmit directly to the satellite. This means, for instance, that the systems in two separate cars can communicate directly with one another without having to first send their data to a central hub.” Not only does this make it easier to communicate, but it also increases data security. Consequently, as well as being suitable for use on water and in the air, satellite communication will soon also be available while driving down bumpy roads.