Satellite digital audio radio service (SDARS) broadcasts digitally encoded audio entertainment material from orbiting satellites or terrestrial repeaters to receivers. XM uses 12.5MHz of spectrum divided between satellites and repeaters, employing QPSK modulation. Repeaters use COFDM modulation. SDARS provides national coverage and many live radio channels, delivering commercial-free, digital quality audio via satellites stationed above the US and repeaters to enhance coverage. XM and Sirius launched competing satellite radio services in the early 2000s, later merging in 2008 with FCC approval.

1. Prof.Minakshi Atre
PVG

4.  Satellite digital audio radio service (SDARS) is
a satellite-based direct-broadcast radio
service
 In SDARS, digitally encoded audio
entertainment material, is broadcast to
earth-based receivers either directly from an
orbiting satellite, or in cases in which the
receiver is in a shielded location from the
satellite, to the receiver via a repeater
station.

5.  1. Frequencies and Channel Bandwidth:
 XM is assigned 12.5MHz of spectrum range
from 2332.5 to 2345MHz centered on
2338.75MHz. (i.e channel BW is 12.5 MHz)
 This spectrum is roughly divided into sixths
 Four bands are assigned to the transmitting
satellite and two are assigned to a terrestrial
repeater network.

6.  In satellite wireless, a repeater (more
frequently called a transponder) receives
uplink signals and retransmits them, often on
different frequencies, to destination
locations.

8.  WCS: wireless communication service
 The Wireless Communications Service (WCS)
is in the 2305-2320 and 2345-2360 MHz
spectrum range.
 The most common use of WCS spectrum is :
 mobile voice and data services, including cell
phone, text messaging, and Internet.

9.  2.Modulation:
 Satellites use QPSK modulation and
 Repeaters use COFDM modulation to realize
the requirements of terrestrial broadcasting.

10.  For decades, to listen to radio
entertainment, you had two choices: AM
radio and FM radio.
 But in the last few years, an entirely new
way to listen to radio has emerged.
 Satellite radio is now available, in a digital
audio format, for subscription through two
services in the US - XM Radio and Sirius
Satellite Radio.

11.  Programming is provided by satellite, not from
local radio broadcasting towers.
 This means that these services can reach the
entire country, accessing a tremendous
audience.
 So rather than listening to music or news on your
local radio station, you are receiving national
broadcasting - similar to what you have been
experiencing with home entertainment television
for decades.
 And many of the music entertainment channels
on satellite radio are actually live radio - not
everything is pre-recorded.

13.  These satellites are stationed above the US,
beaming the radio signal almost everywhere
in the country.
 And there are multiple terrestrial repeaters
that enhance the signal and provide service
where the satellite signal could be blocked
by natural or man-made features.
 This way whenever you want to listen to a
song or a traffic report, it will be available
on your satellite radio.

14.  The signals provided by these services are
high quality, digital audio format.
 Therefore, the sound you can receive will be
far superior to broadcast radio, depending on
your receiver equipment.

16.  XM Satellite Radio and Sirius Satellite Radio
each launched such a service at the
beginning of the 21st century.
 Satellite radio, also called digital radio,
offers uninterrupted, near CD-quality music
beamed to your radio from space.
 They decided to merge in 2007 and FCC
allowed the merger to go forward in 2008