Germany’s Bosch and Geo++, U-blox of Switzerland, and Japan’s Mitsubishi Electric announced the establishment of Sapcorda Services last Tuesday, a joint venture to provide global navigation satellite system (GNSS) positioning services of centimeter-level accuracy via satellite transmission, mobile cellular technology, and the Internet.
Executives of the four companies said meeting the demands of centimeter-scale GNSS positioning required for applications such as autonomous driving necessitated the creation of real-time correction data services.
The U.S.-operated Global Positioning System (GPS) is accurate only to about 10 meters, while Europe’s corresponding Galileo system, with 18 of its 24 satellites currently in orbit, has an accuracy of 1 meter. Yet even 1-meter accuracy is not sufficiently precise when it comes to ensuring that autonomous vehicles, for example, maintain safe lane positioning and avoid certain obstacles.
Details at the Sapcorda announcement were sketchy, and the company said it would provide more information later. Essentially, it plans to augment GPS and Galileo positioning data in Europe by employing surveyed reference stations on the ground. These stations will monitor satellite signal errors, especially errors caused by the ionosphere and the troposphere, which can bend a satellite’s signal. The stations will send the data via the Internet to a master control center that corrects the errors and transmits the results back to the satellite and also to mobile cell towers for broadcasting to user terminals.
According to Yasuhide Shibata, senior general manager of Mitsubishi Electric’s high-precision positioning systems department, error correction and transmission of the corrected data—which is greatly compressed for fast transmission—takes place in real time.
The scheme is similar to Japan’s GPS-augmented Quasi-Zenith Satellite System (QZSS), which aims to provide centimeter-level positioning and navigation services in Japan. The system employs 1,300 reference stations to constantly correct satellite errors. The corrected data is then compressed from an overall 2-megabit-per-second data rate down to 2 kilobits per second for real-time transmission back to the satellite for broadcasting to user receivers.
Shibata noted that Sapcorda-corrected data will be delivered in an open format to encourage system integrators, original equipment manufacturers, and terminal manufacturers to work with its specifications. “The hope is,” said Shibata, “that providing this open format will help create an industry standard.”
On 19 August, Japan’s space agency, JAXA, and Mitsubishi Heavy Industries (provider of rockets and launch services) launched QZS-3, the third of a four-satellite constellation making up the Quasi-Zenith Satellite System. The launched followed a cancellation the previous week due to “the necessity of additional examination around the rocket propulsion system.”
Japan’s centimeter-level navigations system relies on fleet of satellites in geostationary orbit.Erik Vrielink
The fourth satellite is slated for launch in October, and operations are due to begin next year. Later, a further three satellites will be added for backup purposes.
Three of the four satellites will maintain an inclined geosynchronous orbit that traces a north-south asymmetrical figure eight over Japan. The orbit extends as far south as Australia at its widest arc, while its path narrows over Japan. A fourth satellite will augment the system and provide disaster messaging services. This arrangement ensures that at least one satellite is always in view high in the sky above Japan, which explains the name Quasi-Zenith Satellite System.
To date, the Japanese government has budgeted approximately US $1.9 billion to create the QZSS system and the ground support that will augment GPS. In doing so, the government believes that providing centimeter-scale positioning and navigation services will usher in a whole slew of innovative new applications.
For instance, Japanese automakers hope to use high-precision GNSS positioning services, which are necessary to make self-driving car technology safe to use. This is particularly the case in Japan, where much of the country is mountainous and major cities like Tokyo and Osaka are renowned for their dense urban canyons, characteristics that block satellite signals.
Go Takezawa, executive director for QZSS Strategy at Japan’s National Space Policy Secretariat, in updating the press last Tuesday, said that QZSS will help aid the creation of 3D maps, another essential component necessary to make driverless vehicles operationally safe.
Currently, the Dynamic Map Platform Co. (DMPC), a government-backed joint venture between major Japanese auto manufacturers, Mitsubishi Electric, and map-related companies, is creating 3D maps of 30,000 kilometers of Japanese highways. The company is capitalized at 4 billion yen (US $36.4 million) a third of which the Japanese government is funding through the public-private Innovation Network Corp. of Japan, DMPC’s major investor.
Other applications Takizawa cited include precision control of autonomous tractors in agriculture, of machinery used in large-scale construction, and of drones employed in delivering goods to small islands close to Japan. Takizawa noted that tests of all these applications are ongoing, and good results have been obtained in all cases.
This post was updated on 19 August to include the successful launch of the QZS-3 satellite.