Digital Video Broadcast (DVB)

Introduction

The most popular family standard of digital television is the DVB (Digital Video Broadcast). These standards are maintained by the DVB Project and are published by the European Telecommunications Standards Institute (ETSI). However, the DVB standards are used worldwide, not only in the Europe. The minimum video quality provided by the DVB standards is comparable with the DVD (480/576i), but the Full HD (1080p) quality is also supported.

Very high video quality is not the only advantage of the digital television. The DVB uses also much less bandwidth, so it is possible to provide more television channels in the same frequency spectrum. The second advantage is the possibility of encryption. It means that the DVB provider sends the same signal to all clients and the available channels are encrypted on the basis of provided access card.

Satellite digital television

The first satellite digital television standard is DVB-S which was released in 1997. However, the first world’s digital satellite television services were launched in Thailand and South Africa at the end of 1994. Of course, these services were not based on the final version of DVB-S standard, but it was using the newest release of the standard which was available at that time.

About 10 years later (i.e. in 2003) the next version of the digital satellite television standard was developed, i.e. DVB-S2. The idea was to take an advantage of the newest channel coding, modulation and error coding techniques. Therefore, DVB-S2 offers over 30% higher capacity than DVB-S in the same signal reception conditions and using the same bandwidth. The maximum transported capacity is almost 40% higher, but it would require higher satellite’s transmission power or bigger antenna.

The next standard was approved 10 years later (i.e. in 2014) and it is called DVB-S2X what stands for S2 Extensions. DVB-S2X was developed in order to support Ultra HD television channels, so it has up to 51% higher spectral efficiency. However, in order to achieve so high transporter capacity, it is required to receive about 4.5 dB stronger signal than in case of DVB-S2. In normal conditions (i.e. without changing of the receiving antenna and satellite’s transmission power), it is possible to increase the capacity thanks to channel bonding up to 3 satellite channels.

Cable digital television

The most popular standard used in cable networks for digital television broadcasting is DVB-C (Digital Video Broadcasting – Cable). This standard was released in December 1994 and it is still widely used over the whole world. However, more advanced solutions (i.e. more efficient) are required by the industry. Therefore, the new standard, i.e. DVB-C2, was announced in February 2008 and released in April 2009. As the same, as in case of DVB-S2, DVB-C2 offers much higher spectrum efficiency (thanks to more efficient modulation and coding schemes), adaptive modulation and support for wider channels.

DVB-C2 supports 4096 QAM modulation which provides about 60% higher data transmission throughput than 256 QAM modulation used in DVB-C. However, in order to achieve so high performance, the signal to noise ratio has to be about 5 dB higher. Also, thanks to more advanced error correcting techniques, DVB-C2 provides the performance of DVB-C with about 7 dB weaker signal. In case of the same condition, the DVB-C2 provides about 35% higher spectrum efficiency than its predecessor. The minimum required signal strength is about 7 dB lower than in case of DVB-C. In this case, 16 QAM modulation has to be used. Thanks to these advantages, DVB-C2 is cheaper and can be used to build long-distance cable digital television networks.

Terrestrial digital television

The most popular digital terrestrial television system is DVB-T and it was released in 1997. The first broadcast transmission in this technology was launched in United Kingdom in 1998. This standard was developed as the replacement of analogue TV. The DVB-T offers up to 31.7 Mbps capacity using 8 MHz channel. However, the typical achievable data rate is about 24 Mbps. This is enough to broadcast several TV channels in the bandwidth used by a single analogue TV channel. The DVB-T standard was designed for standard-definition television (i.e. SDTV 576i) channels. However, the industry required more efficient solution for high-definition television (HDTV) broadcasting.

Therefore, new standard (DVB-T2) was published in 2009. As in case of DVB-S2 and DVB-C2, the DVB-T2 uses higher order modulations, more efficient coding and much better error correction algorithms. As the result, DVB-T2 offers up to 45.5 Mbps data rate in 8 MHz channel, i.e. the multiplex capacity compared with the DVB-T standard is about 40% higher. The typical achievable result is slightly lower and TV subscribers are able to achieve about 40 Mbps data rate. Also, DVB-T2 provides much better coverage, because the 24 Mbps speed is achievable with signal 6 dB weaker than in case of the DVB-T.

Signal reception

In case of all DVB standards the signal is provided to the receiver by the coaxial cable. This cable can be connected directly to the TV (with required DVB standard support) or to the DVB decoder provided by the TV broadcaster. In both cases, it is possible to measure the signal strength (in dBu or percentages), quality (marked as C/N or in percentages) and BER (Bit Error Rate).

Generally, the most important is the signal quality bar. In order to be able watch HD channels, it is required to have stable C/N (Carrier to Noise ratio) with about 30 dB value and very low BER. In case of terrestrial and satellite system the signal quality can be improved by the proper antenna pointing.