Satellite Telephone

Satellite mobile communications service covers all of Japan including the country's isolated islands by four beams from the geostationary N-STAR satellite. As satellite communication is less affected by geophysical disasters or weather conditions, it provides highly reliable service even during emergencies.

The N-STAR satellite mobile communications system was developed on the principle of sharing the hardware of terrestrial systems in terms of technology. Through integration with the ground network, it provides an efficient and economic system that includes the necessary minimum functions and allows for effective frequency usage and the efficient consumption of satellite power. Moreover, we have also developed various innovations in order to maximize the number of satellite circuits and provide stable service.

As the system operates most efficiently at a low C/N ratio, we adopted /4 shift QPSK and synchronized detection as the modem system, convolutional coding with a large coding gain and Viterbi decoding as the error correcting system. This makes it possible to realize stable operations at a low C/N ratio in the mobile unit. FDMA/SCPC has been adopted as the multiple access system from the viewpoint of developing compact mobile stations and reducing transmission power.

Further, by using half-rate CODEC for voice communications and setting the non-telephone transmission speed at 4.8kbps, we have been able to reduce satellite power per carrier and increase the number of satellite circuits. In addition, greater economy and higher reliability have been achieved by such functions as "shut-out control" that protects the satellite by blocking inputs that exceed the number of circuits, a "non-telephone trunk" that controls data communications between the terrestrial and satellite systems, as well as "VOX control" that transmits only in the case of voice communications.

Configuration of N-STAR Satellite Mobile Communications System

Created 1999/03

Updated 2004/03