Satellite Radio: The Next Communications Revolution? David Bultman

Challenges In Satellite Radio There are three general problems with satellite reception: Blockages Foliage Multipath Fading

Blockages The target of satellite radio is a mobile platform This rules out the use of special high gain antennas and expensive satellite tracking systems The important factors to think about when considering blockages are the movement of the receiver, the movement of the satellite, and the angle of elevation of the satellite

Foliage Foliage is similar to a blockage with a few exceptions Foliage can block or attenuate a signal The amount of attenuation can depend on the type of foliage, the frequency of the signal, and the incident angle Foliage can also reflect a signal with a random amount of attenuation and phase shift

Multipath Fading Multipath Fading occurs multiple forms of the original signal are received

Solutions – Spatial Diversity Spatial Diversity = Instead of having a single signal source, use multiple signal sources spread out Spatial Diversity helps fix all three of the problems

Solutions – Frequency Diversity Frequency Diversity = Sending the same information on two separate and unrelated frequencies (preferably also spatially diverse) Frequency Diversity is aimed at fixing multipath fading

Solutions – Time Diversity Time Diversity = Delaying one of two spatially diverse signals in time before its broadcast Time Diversity is aimed at eliminating audio outages when both broadcast signals are blocked simultaneously

Solutions – Repeater Stations Repeater Stations are used in areas where even the combination of the other three solutions may not yield a “good” signal

XM Radio’s System Two geostationary satellites with a 45 degree angle of elevation Each satellite emits about 10MW of signal energy Approximately 1500 low power repeater stations serving 70 markets

Sirius Radio’s System Three satellites in an inclined elliptical orbit Each satellite spends about 16 hours over the US, with two satellites always above the equator

Sirius Radio’s System The satellites are inclined at 60 degrees The satellites are of lower power than XM Radio’s 105 high power repeaters serving 46 markets

The Future? From all indications the audio quality is superb with both providers The tests will be subscriber numbers and the possibility of terrestrial radio adding digital signals to their broadcasts to compete