TOKYO-The Japanese government has begun development work for a 40-billion-yen (US$317 million) futuristic mobile communications system using a geostationary satellite.
If the technology is adopted by cellular carriers, handheld satellite mobile phone users in every part of Japan will be able to communicate with each other at 5.6 kilobits per second (kbps) for voice, with CD-like quality, and at 32 kbps for data. The satellite system is scheduled to be launched in 2002, and commercial service could begin 2005.
“When commercial services start based on the [new] technology, all of the Japanese will be able to enjoy cellular services,” said Yoshiaki Takeuchi of the Satellite Communications Policy Division at the Ministry of Posts and Telecommunications.
The government considers the new system vital for establishing universal mobile service in Japan. Currently, 15 percent of the 3,300 municipalities in Japan are not covered by cellular. To eliminate any gaps in cellular coverage, the government has invested 30 billion yen (US$238 million) to construct base stations in rural areas. Although the MPT will continue such efforts, it still expects about 10 percent of the municipalities will not be covered by traditional cellular service by the end of 2000 because of geographic constraints.
A geostationary satellite system is a cost-effective solution for Japan to provide full coverage. Compared with low-earth-orbit (LEO) or medium-earth-orbit (MEO) satellite communication programs, this type of satellite system can be launched at a lower cost, say officials. It also is less expensive to deploy than traditional cellular systems. According to one estimate from the National Space Development Agency of Japan (NASDA), investment for facilities and equipment for existing cellular systems is 145,000 yen (US$1,150) per subscriber; for the satellite system, the same figure is projected at 130,000 yen (US$1030).
Since conventional cellular systems are used efficiently, MPT believes the GEO mobile system could be a supplemental service. In addition, the project has been designed to serve limited regions using one GEO satellite, but its services could be extended by increasing the number of GEO satellites.
Based on basic research and design completed by various organizations, manufacturing firms such as Mitsubishi Electric Corp., Fujitsu, Toshiba Corp. and NEC Corp. will construct the satellite. The assembled model, to be called the Engineering Test Satellite (ETS)-VIII, will be launched from NASDA’s Space Center on Tanegashima in 2002.
Studies on the mission payload of the geostationary satellite have been launched at the Communications Research Laboratory (CRL), the MPT’s sole laboratory, and the Advanced Space Communications Research Laboratory (ASC). The ASC was founded in 1993 to develop the ETS-VIII. Up to 70 percent of the firm’s 8.3-billion-yen (US$66-million) research and development budget came from the Japan Key Technology Center. NASDA is developing the bus system and antennas.
The ETS-VIII is a 3-ton class geostationary satellite. Commercial service is expected to provide service to 3,000 channels, or 300,000 customers, using a bandwidth of 25 MHz on the S-band.
One of the most remarkable features of the satellite is its huge reflectors. To reduce the size of user terminals that would be needed, the satellite has a pair of large deployable reflectors on the east and the west sides. Each reflector has a diameter of 13 meters-the largest in the world.
The communications payload also will be equipped with an on-board processor (OBP), a phased-array feed and a feeder-link subsystem. Conventional satellite communications systems employ a double-hop system that shuttles the beam between the ground station and the satellite twice. Equipped with the OBP, the new satellite system realizes a one-hop system, in which the beam shuttles only once, thus eliminating the need for ground stations and significantly reducing the delay time to about 0.3 seconds.
The new system is durable for natural disasters, such as earthquakes, since it does not need the ground stations.
The CRL; NTT Wireless Laboratories, one of the NTT’s 14 laboratories; and ASC will develop key technology for the terminals, including handheld, laptop and on-board models.
The handheld terminals will be the same size as the present handheld terminals for the Iridium project. Compared with current laptop satellite cellular terminals provided by NTT DoCoMo, the new laptop terminals will have a much higher data transmission speed of 512 kbps. NTT DoCoMo is providing both laptop and on-board terminals. The laptop model will weigh between 2 kilograms and 2.7 kilograms and can transmit data at 4,800 bps.
