Beam patterns: B1 shows a directional beam, in which all of the energy is focused toward one antenna for a fast signal. B2 shows an omnidirectional beam that encompasses many stations to avoid dropped connections. B3 shows R2D2’s method of combining the two techniques to get the best signal.
Additional R2D2 software at the base stations coordinates between selected stations. R2D2 designates one station as the anchor, which routes the information to and from the Internet. The base station that gets the full packet of information first sends it to the anchor.
The researchers also created a software program that builds a database out of the best paths to use at different segments along a road, based on past use. This database, called the Beam Manager, divides a road into segments and assigns base-station groups to users depending on their location.
The group tested its system to see how much data R2D2 could transfer from a relay to a base station, compared with other new systems. The researchers did this by setting up four Wi-Fi base stations (using Linux device drivers) in a parking lot and along a street. To compare, they also tested a system called Mobisteer, which uses directionality to focus the antenna’s beam, and Microsoft’s ViFi, which uses diversity to transmit to several antennas at once. The researchers found that in about 200 seconds, R2D2 uploaded 216 megabytes of data while moving along at 15 to 20 miles per hour. That’s about 150 percent more than Mobisteer and about 40 percent more than ViFi.
Currently, most systems use cellular stations to access the Internet in vehicles. Before R2D2 and other Wi-Fi-based systems can be truly useful, cities and roads will need more Wi-Fi infrastructure as well.
Hannes Hartenstein, a professor at the University of Karlsruhe, in Germany, who has shown that diversity improved vehicle-to-vehicle communication, says that the R2D2 results look valid. He adds that the next step would be to see how this works for downloading data.