NTT started development of a multimedia satellite communication system to p
rovide a medium for Internet access in 1995. This system, which entered com
mercial service in 1998, uses a hybrid network consisting of a high-speed s
atellite forward link and terrestrial access links. To meet the increasing
demand for low-cost and ubiquitous access links, a second-generation system
equipped with satellite transmitting functions is now being developed. The
user terminal design calls for a DTH-sized receiver antenna and a transmis
sion power of less than 0.1 W, which will make it suitable for use in homes
and small offices. The access link signals from the user terminals are sup
erimposed onto the high-speed TDM forward link signal for efficient use of
the frequency band. The transmission power from the user terminal is signif
icantly low compared to that of the forward link signal, a novel interferen
ce cancellation technique is introduced. A channel assignment scheme called
"channel reservation with rapid release" is introduced for both efficient
use of the channels and higher transmission throughput. The forward link si
gnal is completely compatible with the first-generation system, and the dat
a rate is about 30 Mb/s.
The paper describes the system's configuration, the central earth station's
configuration, and the key technologies of the radio system and access con
trol system. (C) 2001 International Astronautical Federation. Published by
Elsevier Science Ltd.