Digital TV reception: The global challenge

The world is going digital. This is a commonly used phrase but sounds simpler than it is in reality. Throughout the last 15 years hundreds of companies have been involved in defining standards for the reception of digital TV. Digital TV reception nowadays is available through different transmission media such as cable and satellite as well as over the air. With the world getting smaller due to better communication you might expect that when defining new standards a 'global standard' would be the goal. However, it is nothing like that. Just like good old analog TV where we had NTSC, PAL in different variants and SECAM, digital TV knows many different standards as well, some of which are still in the definition phase. Of course politics play an important role in the standard definition process but in this article we will explain how different target applications and environments have a strong influence on the chosen technologies.

Digital TV transmission media
In order to make digital TV available to the end consumer, the TV content needs to be encoded. There are different encoding schemes available and the main purpose of the encoding process is to digitize the information with the lowest possible bit-rate at the highest possible quality. The most common method is MPEG (Moving Picture Expert Group) where motion vectors are used to determine where parts of the picture are moving. By transmitting picture information together with motion vectors, the decoder can retrieve the original content again. Most widely used nowadays is the MPEG2 standard but with the trend of bigger screens with higher resolution and the ever increasing demand for more bandwidth, there is a requirement for improved encoding schemes such as MPEG4.

Once the content is digitized with the above mentioned techniques it needs to be transmitted. Transmission can be done through Satellite, Cable, and over the air. Since all transmission channels have different limitations different technologies are used to bring the digital content to the consumer's home.

Figure 1. Three methods for transmitting information: Satellite, Cable and Terrestrial.