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Communications Commission (FCC) allocated a spectrum in
the “S” bandwidth (2.3 GHz) for nationwide broadcasting of
satellite-based digital audio radio service (DARS). In 1997, the
FCC gave licenses to use part of that spectrum to two companies:
CD Radio (now Sirius Satellite Radio) and American Mobile
Radio (now XM Satellite Radio). The two companies had
similar approaches to their implementation of satellite radio.
XM Satellite Radio uses two Hughes/Alcatel satellites, placed
in parallel geostationary orbits. The satellite digital audio radio’s
(SDAR) signal architecture uses spatial, time and frequency
diversity to improve the reception performance in a mobile
environment. Programming is repeated from three sources: two
satellite paths and one terrestrial path. Sirius Satellite Radio uses
three SS/L-1300 satellites to form an inclined elliptical satellite
constellation (Fig. 5). The elliptical path of the satellite constellation
ensures that each satellite spends about 16 hours a day over
the continental United States.
XM Satellite Radio’s ground station transmits a signal to the
satellites, which bounce the signals back down to radio receivers
on the ground. In urban areas, where buildings can block out
the satellite signal, the broadcast is supplemented by ground
transmitters. The radio receivers are programmed to receive
and unscramble the digital data signal, which contains up to 100
channels of digital audio (local- and non-local-based programs
available with large program-type selections). In addition to the
encoded sound, the signal contains all the metadata for the audio
content such as song title, artist and genre.
The Sirius Satellite Radio receiver includes two parts: the
antenna module and the receiver module. The antenna module
picks up signals from the ground repeaters or the satellite,
amplifies the signal and filters out any interference. The signal
is then passed on to the receiver module. Inside the receiver
module is a chipset consisting of eight chips. The chipset
converts the signals from 2.3 GHz to a lower intermediate
frequency. Sirius Satellite Radio provides high audio quality
with an output of downlink processor signal-to-noise radio of
85 dB. Its frequency response from 100 Hz to 15 kHz is
within +/- 3 dB. The Sirius Satellite Radio also provides over
65 commercial-free channels and dynamic bandwidth allocation
for very high quality music programs.
The XM Satellite Radio receiver system includes the
antenna module and a remote receiver module. A separate
receiver box is used to receive the satellite and terrestrial
signals. The remote receiver box makes the radio capable of
receiving the proprietary satellite signal through a custom
chipset. System mechanization calls for an XM Satellite Radio
receiver that will interface with the radio receiver packaged in
the vehicle’s instrumentation panel by means of a data link.
Satellites provide the primary coverage while the repeaters are
used to fill in areas where the vehicle will be blocked from the
Fig. 2: Twenty-four satellites orbit the earth as part of the GPS (Figure
credit: Peter H. Dana).
Fig 3: The navigation screen on CG’s CAN-based navigation radio.
Fig. 4: A cluster navigation display screen in a Chrysler 300.
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