HEI -- Direct Broadcast Satellite (DBS) and Broadcasting Using Video Compression

HEI consultants have prepared this paper about direct broadcast satellite technology and MPEG2 video compression. This paper was originally prepared focusing on the U.S. DirecTV full coverage DBS or direct broadcast satellites. This discussion also applies to the DirecTV spot beam satellites used for delivery of local market broadcast stations across the USA.

Generally, other DBS providers including Dish Network in the US as well as Bell ExpressVu and StarChoice in Canada use similar technologies. DirecTV 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 Dish Network, Bell ExpressVu or StarChoice.

These satellite systems operate using microwave frequencies what is known as "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 three primary high-power satellites, together with a spot-beam satellite 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 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 secondary 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.