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Digital Video Broadcating DVB Tutorial Includes: DVB basics DVB-T DVB-T2

DVB-T or Digital Video Broadcast - Terrestrial is the most widely used digital television standard in use around the globe for terrestrial television transmissions. It provides many facilities and enables a far more efficient use of the available radio frequency spectrum than the previous analogue transmissions.

The DVB-T standard was first published in 1997 and since then it has become the most widely used format for broadcast digital in the world. By 2008, it was the standard that was adopted in more than 35 countries and over 60 million receivers deployed and in use.

DVB-T makes use of many modern technologies to enable it to deliver high quality video in a broadcast environment.

The DVB-T transmission is capable of carrying a very significant level of data. Normally several television broadcasts may be carried on a single transmission and in addition to this several audio channels may be carried as well. As a result each transmission is called a multiplex.

One of the key elements of the radio or air interface is the choice of the modulation scheme for DVB-T. In line with many other forms of transmission these days, DVB-T uses OFDM, Orthogonal Frequency Division Multiplex.

In order that the DVB-T network is able to meet the requirements of the operator, it is possible to vary a number of the characteristics:

By altering the various parameters of the transmission it is possible for network operators to find the right balance between the robustness of the DVB-T transmission and its capacity.

One of the advantages of using OFDM as the form of modulation is that it allows the network to implement what is termed a single frequency network. A single frequency network, or SFN is one where a number of transmitters operate on the same frequency without causing interference.

many forms of transmission, including the old analogue television broadcasts would interfere with one another. Therefore when planning a network, adjacent areas could not use the same channels and this greatly increased the amount of spectrum required to cover a country. By using OFDM an SFN can be implemented and this provides a significant degree of spectrum efficiency improvement.

A further advantage of using a system such as DVB-T that uses OFDM and allows the implementation of an SFN is that very small transmitters can be used to enhance local coverage. Small "gap fillers" may even be used to enhance indoor coverage for DVB-T.

Another facility that is allowed by DVB-T is known as Hierarchical Modulation. Using this technique, two completely separate data streams can be modulated onto a single DVB-T signal. A "High Priority" or HP stream is embedded within a "Low Priority" or LP stream. Using this principle DVB-T broadcasters are able to target two different types of receiver with two completely different services.

One example where this could be used is for a DVB-H mobile TV service optimised for more difficult reception conditions could be placed in the HP stream, with HDTV DVB-T services targeted to fixed antennas delivered in the LP stream.

DVB-T is now well established. Many countries, including the UK are moving towards a complete switch-over from analogue to digital, with a resultant digital dividend releasing a significant amount of bandwidth for other services. However as DVB-T has now been in use for ten years a new standard, which is a development of the original DVB-T standard known as DVB-T2 is being developed. This would have backwards compatibility, but allow additional services and flexibility as well as a number of features to future-proof it.