Grundig Digital Radio manual Sirius Overview

DIGITAL RADIO GUIDE SATELLITE TRANSMISSION - SIRIUS / XM

reduces the need for terrestrial repeaters and lowers the probability of outages from blockage and foliage attenuation. Currently, Sirius employs approximately 100 repeater sites and XM approximately 800.

5.2.1Sirius Overview

The first Sirius spacecraft was launched on July 1, 2000. Exactly five months later, on December 1, the third spacecraft was launched, completing the three satellite S DARS (Satellite Digital Audio Radio Service) constellation. The three spacecraft are deployed in inclined, elliptical, geosynchronous orbits, which allow seamless broadcast coverage to mobile users in the contiguous United States. Terrestrial broadcast repeaters provide service in urban cores. The system is in operation, providing the first ever S-DARS service.

The constellation design results in satellite ground tracks over North America with two satellites always above the equator. High elevation look angles from the mobile ground terminals to the satellites minimize performance degradation due to blockage, foliage attenuation and multipath.

The spacecraft were built by Space Systems/Loral using the 1300 bus modified for operation in high inclination orbits. Each spacecraft was launched using a dedicated Russian Proton booster. The satellite payload is a bent pipe repeater using 7.1 GHz for the uplink and 2.3 GHz for the broadcast transmission. The repeater high power amplification stage consists of 32 Traveling Wave Tube Amplifiers phase combined to yield a total RF output power of nearly 4 kW at saturated operation. The satellite antennas are mechanically steered to maintain the transmit beam centered on CONUS (Contiguous United States) and the receive beam centered on the uplink earth station located in Vernon Valley, New Jersey.

The satellite payload design and performance are described. The principal spacecraft bus systems are described with emphasis on improvements made for operation in the inclined, elliptical geosynchronous orbits.

The two active satellites transmit the same signal at different frequencies with a 4-second delay between them, which is inserted at the uplink earth stations. In the urban core of large cities where satellite blockage can be very high, terrestrial transmitters rebroadcast the satellite signal. The satellites’ different orbital positions, transmission frequencies and signal delay provide the diversity while the receivers’ equalizer and maximal ratio combiner (e.g., sums the two satellite and terrestrial repeater signals) provide the other listed techniques. Moreover, the achievement of high elevation angle is an extremely important attribute, and its achievement required the adoption of a unique orbital configuration.

Originally Sirius Satellite Radio had planned for geostationary satellites at 80° and 110° West longitude. The resulting low elevation angles to mobile users in the northern third of CONUS would cause service outages whose number and duration result in an unsatisfactory quality of service irrespective of the diversity employed and the satellite Effective Isotropic Radiated Power (EIRP) level. Satisfactory service might be achieved by deploying an enormous number of terrestrial repeaters but this was judged impractical given the economic and regulatory issues involved. Consequently, an orbital constellation was designed by Sirius Satellite Radio and implemented by Space Systems/Loral (SS/L) that provides high elevation angles over this critical area.

70