Acleris
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1. Introduction:

Acleris consultants have prepared this paper about direct broadcast satellite technology and MPEG2 (pronounced em-peg two) video compression. DirecTV's full coverage DBS or direct broadcast satellites system was selected as the model for this paper as it is by far the largest system, with more satellites, greater bandwidth, higher transmit power and more subscribers than the others sharing the market. Information generally equally applies to both the U.S. DirecTV full coverage direct broadcast satellites and the spot beam satellites used for delivery of local market broadcast stations across the USA.

Generally, other DBS providers including Dish Network in the US and Bell ExpressVu and StarChoice in Canada use similar technologies. Similarly, DBS systems in other jurisdictions across the world use the same technologies.

These direct broadcast satellite systems operate using microwave frequencies in what is known as the "Ku-band". The downlink, from satellite to earth, operates at frequencies between 12.2 gigahertz (GHz) and 12.7 GHz. DirecTV's major full continental USA coverage is from a group of three primary high-power satellites, together with spot-beam satellites for city-by-city local coverage. This primary group of satellites form a mini-constellation that can be simultaneously viewed by small, fixed, round DBS antennas such as those provided by RCA, Hughes and others.

The basic receiver system includes the IRD or integrated receiver decoder (the set-top box), and a small 18" x 20" (45.7cm x 50.8cm) antenna having an approximate gain of 34 dB at 12.5 GHz, and with a half-power beamwidth of about 3.5 degrees. Each satellite has 16 or more transponders, analogous to channels on a television receiver except that each transponder can carry many television signals simultaneously. Each transponder operates at a data rate of 40 megabits per second (40 Mbps).

DirecTV also has other satellites providing HDTV or High Definition Television, additional standard services like NASA-TV, multilingual services and bidirectional Internet access. These other satellites are at a different orbital position, requiring use of a larger oval-shaped dish for reception.

C O N T E N T S

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