Skip to main content

RF Shorts for April 24, 2014

Japan Plans Centimeter-Resolution GPS

 Urban canyons can significantly reduce GPS location accuracy as buildings block the signals from some GPS satellites and cause reflections. Engineers at Tokyo-based Mitsubishi have come up with a way to improve accuracy using four satellites tracing a figure-eight orbit configured so that one satellite is always high in the sky over Japan. A master control center compares the GPS satellite's signals received by reference stations with the distance between the stations and the satellite's predicted location and send that data to users' receivers for error correction.

"GPS positioning can be off by as much as 10 meters due to various kinds of errors and in Japan, with all its mountains and skyscrapers blocking out GPS signals, positioning is not possible in some city and country locations," said Yuki Sato, a research engineer in Mitsubishi Electric's Advanced Technology R&D Center. "Errors can be caused, for example, by the satellite’s atomic clock, orbital shift, and by Earth’s atmosphere, especially the ionosphere, which can bend the signal, reducing its speed."

A private company, Quazi-Zenith Satellite System Services, was established to construct the ground portion of the system, which will include 1,200 precisely surveyed reference stations. The first satellite, QZS-1, was launched in September 2010 by the Japan Aerospace Exploration Agency (JAXA). Three additional satellites are scheduled to be in place by the end of 2017. The satellites will provide real-time correction data. Ryoichiro Yasumitsu, a deputy chief manager in Mitsubishi’s Space Systems Division said that in QZS-1 trial tests the average accuracy is about 1.3 centimeters horizontally and 2.9 cm vertically.

More details are available in the IEEE Spectrum article by John Boyd: Japan’s Plan for Centimeter-Resolution GPS -- $1.2 billion system of satellites and ground stations would give unprecedented accuracy.

Wireless Charging System Delivers 209 Watts Across Five Meters

Researchers at the Korean Advanced Institute of Science and Technology (KAIST) have developed a "Dipole Coil Resonant System" that’s able to deliver 209 Watts of power over a distance of five meters. Chun T. Rim, professor of Nuclear & Quantum Engineering at KAIST, said the system could power a large LED TV, as well as three 40 Watt fans from five meters, or it could charge 40 smartphones simultaneously.

DCRS improves on MIT's Coupled Magnetic Resonance System (CMRS) by reducing the system's size and improving transfer efficiency. DCRS swapped the large loop-shaped air-core coils used in CMRS for compact ferrite core rods with coil windings in the center.

The DCRS is three meters long, 10 centimeters wide and 10 centimeters high. When operated at 20 kHz, the maximum output power was 1,403 Watts at three meters, 471 Watts at four meters and 209 Watts at five meters. For a power level of 100 Watts, the electric power transfer efficiency was 36.9 percent at three meters, 18.7 percent at four meters and 9.2 percent at five meters.

"Our technology proved the possibility of a new remote power delivery mechanism that has never been tried at such a long distance," said Rim said. "Although the long-range wireless power transfer is still in an early stage of commercialization and quite costly to implement, we believe that this is the right direction for electric power to be supplied in the future. Just like we see Wi-Fi zones everywhere today, we will eventually have many Wi-Power zones at such places as restaurants and streets that provide electric power wirelessly to electronic devices. We will use all the devices anywhere without tangled wires attached and anytime without worrying about charging their batteries."

Additional information and photos of the DCRS are available in the news release Prof. Chun T. Rim - Wireless Power Transfer Achieved at 5-meter Distance. Comments and RF related news items are welcome.

Email me at

Doug Lung

Doug Lung is one of America's foremost authorities on broadcast RF technology. He has been with NBC since 1985 and is currently vice president of broadcast technology for NBC/Telemundo stations.