Uncompressed video signals require a lot of bandwidth -- so much, in fact, that satellites can't handle receiving and transmitting that much information at the same time. That's why satellite service providers compress video signals, especially when they're high-definition video. They use a compression system standardized by the Moving Picture Experts Group (MPEG).
There are a few different MPEG encoding standards. You're probably familiar with MP3 files, which are audio files that use the MPEG-1 standard. Until recently, satellite systems compressed video using the MPEG-2 standard, which reduces video size by a factor of about 55:1. Today, DISH network and DIRECTV, the two major satellite service providers in the United States, use the MPEG-4 compression standard. This format is more efficient than MPEG-2 and is better suited for complex, fast-moving images like those in sporting events and action movies.
Before the switch to MPEG-4 compression, satellite service providers could only offer a few HD channels due to the demand on system bandwidth. As cable companies began to develop HD packages, satellite systems had to look for new ways to deliver HD signals to customers in order to stay ahead of the competition. Both DIRECTV and DISH Network have upgraded to the MPEG-4 format, which allows both companies to provide more HD channels by streaming them more efficiently. Unfortunately, this upgrade also means that customers have to upgrade their equipment in order to view that programming.
Satellite companies had designed customer dishes and set-top boxes to receive and convert signals broadcast in the MPEG-2 format. The MPEG-4 format wasn't at all like MPEG-2, so customers' existing equipment couldn't receive and decode the new signals. These customers had a choice to make: stick with the old service and keep their old equipment, or pay money to upgrade and access more HD content. While satellite service providers are currently leaving the choice up to individual customers, in the future all providers will use the MPEG-4 format. At that point, old equipment will become useless.
Apart from the different encoding techniques, satellite HD receivers are similar to standard set-top boxes. The video signal arrives at the customer's dish and travels through a cable to the receiver. The receiver has three jobs:
- Decrypt the signal. In order to thwart would-be signal thieves -- people who use hacked dishes and receivers to steal satellite service -- satellite service providers scramble television signals using encryption codes. The companies sell or lease receivers that include a chip designed to decrypt incoming signals. This way, only customers with the right equipment will be able to view incoming signals.
- Decompress the signal. Compression formats like MPEG-4 make it possible to transport an HD signal from a provider to a customer, but televisions can't interpret compressed signals. The receiver must convert the signal from MPEG-4 to its uncompressed state.
- Feed the signal to the television. Once the receiver decrypts and decompresses the signal, it sends it on to the customer's HDTV.
In the next section, we'll learn about the state of satellite HD service today.