Page 73 - Communications Satellites Global Change Agents

2. EVOLUTION OF SATELLITE TECHNOLOGY 49

intersatellite delivered services. The fixed satellite service refers to point-to-point
communications links, which means for transmissions to and from ground termi-
nals that remain fixed in place.
The other types of satellite services are precisely defined by the ITU and are
discussed in depth in chapter 3. The most important of these include mobile satel-
lite services (i.e., point-to-point communications links where one or both ends of
the link are moving during transmissions) and broadcast satellite services (i.e.,
point-to-multipoint where a program is radiated over a "service area" to many re-
ceive-only terminals). In recent years, however, these distinctions have started to
become less clearly defined. For instance, some satellite operators have used FSS
frequencies to provide broadcasting and mobile satellite services. Even more re-
cently, it has become possible to provide thin route return channels associated
with broadcast services, which is known as Digital Video Broadcast with Return
Channel Service (DVB-RCS).
Historically speaking, FSS started with the Early Bird satellite, which was the
first type of space communications service to be implemented for domestic and
international applications. As noted earlier, satellite ground antenna systems had
to be large. These were also difficult to point and steer, and they were somewhat
cumbersome to operate to achieve adequate power levels to communicate with
the GEO satellites. In the early days of operations, satellite ground antennae re-
quired reflectors that were literally hundreds to thousands times the size of most
user terminals today in terms of surface area.
Frequency bands allocated by the ITU for the FSS services have continued to
expand from the days when the first serious allocations were made at the Extra-
ordinary Administrative Radio Conference held in Geneva, Switzerland, in 1959.
Today, the most important allocations are those in the so-called super high fre-
quencies (SHF). This band ranges from 3 GHz to 30 GHz, but there are now also
opportunities to use the so-called extremely high frequency bands from 30 GHz to
300 GHz with allocations in the Ka, Q/V, and W bands.
The FSS allocations are defined as follows: C-band (6 GHz uplink/4 GHz
downlink), Ku-band (14 GHz/12 GHz), Ka-band (30 GHz/20 GHz), Q/V-band
(48 GHz/38 GHz), and W-band (92 GHz/82 GHz). A GigaHertz (GHz) is a billion
cycles per second. This means that all the frequencies used for satellites are oper-
ating at small wave lengths of a meter to a centimeter in size. As the demand for
frequency increases, it seems possible that satellites will actually start to use fre-
quencies above 30 GHz and thus start to use wavelengths that are so small that
they are in the millimeter range.
First-generation FSS satellites operated in C-band (6 and 4 GHz) beginning
in 1965. New and replacement systems began to utilize Ku-band (14 and 12
GHz) in the 1980s. Today, there are over 200 communications satellites offering
FSS in either the C-band, Ku-band, or hybrid systems operating in both. Only a
limited number of Ka-band systems (30 and 20 GHz) are so far deployed with
the Astra system beginning service in Europe at the start of 2002 and with