g News and MTV Asia, among others. Technically, the Sirius Satellite and XM Satellite systems are unique in a number of ways. This is so not just with respect to existing broadcasting systems and the many types of satellite systems (broadcast and otherwise) currently in use, but also with respect to one another. Because these systems are designed to serve primarily mobile users and are targeting a consumer market, the individual receivers need to cost less than any satellite receiver ever built. They cannot rely, for example, on high-gain antennas with costly antenna-tracking devices to keep the antenna pointed at the satellite, the setup used for other mobile satellite systems like Inmarsat, which serves maritime and other commercial markets. (http://www.wirelessnewsfactor.com/perl/story/16799.html#story-start) Another consequence of mobile reception, for automobiles in particular, is that the satellite signal will be intermittently blocked from view by buildings or trees as the vehicle moves. The magnitude of this problem is a function of the latitude of the receiver because this establishes the elevation angle of the satellite with respect to the horizon. The farther north one proceeds, the lower in the sky the satellite appears and the more susceptible it is to being blocked from view. For both systems, the antenna on the receiver is of the low-gain, nearly omni directional variety, its pattern shaped like a hemisphere. So obstructions notwithstanding, the satellite will be in view of the antenna regardless of the vehicle's position. In the XM system, two satellites in a conventional geostationary orbit, one at 85 W longitude and the other at 115 W longitudes, are used. These locations afford optimum coverage of the United States. According to XM, these are the "most powerful satellites in the entertainment industry," helping to compensate for the relatively low gain of the vehicle's antenna. Three specific tech...
