Technology
The Sirius signal is separated into three carriers, one each for the two satellites, and the third for the terrestrial repeater network where available. Sirius receivers decode all three 4 MHz carrier signals at once to achieve signal diversity. This is in contrast to XM which uses six carriers and decodes three 2 MHz carriers to economize on receiver power consumption and complexity at the cost of channel-changing speed. There is an intentional four-second delay between the two satellite carrier signals. This enables the receiver to maintain a large buffer of the audio stream, which, along with forward error correction, helps keep the audio playing in the event that the signal is temporarily lost, such as when driving under an overpass or otherwise losing line-of-sight of any of the satellites or ground repeater stations.
A third, separate signal is uplinked to the AMC-6 Ku-band satellite and received by 36-inch (910 mm) satellite dishes for the ground repeater network. This third signal is broadcast on a third segment of the signal.
Read more about this topic: Sirius Satellite Radio
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