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Sec. 8–5 Satellite Communication Systems 595
of service provided by the long-distance public telephone network [Dorf, 1993, p. 2201;
Maral, 1995; Rana, McCoskey, and Check, 1990]. For more information on VSAT systems,
see [Pratt et al, 2003].
Satellite Radio Broadcasting
Satellite Digital Audio Radio Service (SDARS) is the FCC term for using satellites to broadcast
multiple digital audio streams to subscribers. Typically the charge to a subscriber is
around $13.00 per month for about 100 audio channels. The audio consists of music, news,
sports, weather, and other entertainment channels. In the United States, the FCC licensed two
providers: Sirius Radio and XM Radio. In July 2008, Sirius acquired XM and the combined
company is called Sirius XM Radio, Inc. Some of the technical parameters for these SDARS
systems are shown in Table 8–3.
Sirius uses three satellites placed in elliptical orbits each with a period of 24 hours such
that an individual satellite remains over a site for about 16 hours at a time. At any time, two of
TABLE 8–3
U.S. DIGITAL-AUDIO SATELLITE SYSTEMS
Satellite Parameters Sirius Radio Satellite System XM Radio Satellite System
Number of satellites 3 2
Satellite transmit power 3kW EIRP 228W (TWT output)
Satellite orbit
Elliptical
16 hours overhead
Geostationary, satellites at
85°W and 115°W longitude
Elevation angle to satellite 760° typical
745° typical
Uplink frequencies 7,060.0–7,072.5 MHz 7,050.0–7,075.0 MHz
Downlink frequencies
2,320.0–2,324.0 MHz
and 2,328.5–2,332.5 MHz
2,332.5–2,336.5 MHz and
2,341.0–2,345.0 MHz
Downlink signal bandwidth 4.2 MHz 2 × 1.84 MHz
Satellite output modulation TDM> QPSK
TDM>
QPSK
TDM data rate a
4.4 Mb> s
4.0 Mb>
s
Source data coding Lucent PAC b Lucent PAC b
Number of TDM music channels about 50 about 50
Music channel data rate
64 kb> s (variable)
64 kb>
s (variable)
Number of TDM talk channels about 50 about 50
Talk channel data rate
24 kb> s
24 kb>
s
Terrestrial Repeater Parameters
Number of repeaters about 105 in 46 cities about 1,500 in 70 cities
Repeater EIRP 5 kW per antenna sector most at 2kW but … 10 kW
Output frequencies 2,324.0–2,328.5 MHz 2,336.5–2,341.0 MHz
Repeater modulation
TDM> OFDM
TDM>
OFDM
Modulation delay c 4–5 sec 4–5 sec
a Before FEC. Concatenated coding is added for FEC: Reed-Solomon outer code, rate 12; convolutional inner code
b PAC = Perceptual Audio Codec
c with respect to the satellite modulation