What is DVB-C - description and specifications of the digital format

Digital Video Broadcasting - Cable (DVB-C), a digital video transmission system, founded in February 1994 on the European standard ETS 300 429. The innovation for TV, sound, data and framing is developed under the auspices of the European Broadcasting Union (EBU) and the European Institute Telecommunication Standardization (ETSI). Considering what DVB-C is, it should be said that it is part of the DVB standard, which defines the modulation of MPEG-2 frames depending on the type of broadcast.

History of the standard

It consists of a variety of TVs: satellite (DVB-S), cable (DVB-C) and VHF / UHF (DVB-T). The new generation of television signals is based on digital data compression and transmission. This provides higher image quality and better bandwidth utilization than classic analogue color television broadcasting standards such as PAL, NTSC and SECAM.

In January 1995, a set of standards that define a new digital video broadcasting system were published as part of the DVB project, organized by the EBU. Since 1996, DVBs have been the technical basis for the implementation of digital TV transmission in the EU in many countries of the world, including Russia. The United States has its own standard for terrestrial HDTV, which is based on MPEG-2, uses a modem and audio encoder.

Particular attention in the European classification is given to the cable standard. What is DVB-C? Answering this question, it should be noted that modern DVB describe the transmission of digital TV via satellite and cable. It covers system design and a high-bandwidth transmission modem, as well as several auxiliary functions such as teletext, electronic program guide, and conditional access. The system is an ISO MPEG-2 algorithm.

Building blocks

To understand what DVB-C is, they study the elementary circuit. The block diagram of a DVB receiver consists of a cable or antenna:

• Receiver - demodulation - error correction - additional access control and encryption module.
• MPEG demultiplexer.
• MPEG video decoder.
• MPEG audio data decoder.
• Interface.
• Encoder RGB / S-Video / PAL / PAL.
• A personal computer or modem, and such a DVB-C that provides compatible operation.
• TV, VCR.
• Hi-Fi system.

Representatives of the first generation of consumer DVB receivers consisted of a small enclosure containing a receiver and the above MPEG decoder.

The receivers have a data transmission system, interfaces for personal computers and other multimedia systems (EIA-232-E), one or more slots for ISO 7816 chip cards, PCMCIA type 2 connectors for a control module for access to pay TV, as well as such DVB- C in the TV, which can provide cable connection. Additional interfaces may include digital audio.

Encapsulation MPEG-2

The DVB project did not define its own image encoding algorithm, but chose a profile (subset) of the international standard ISO / IEC 13818, commonly called MPEG-2 in ETR 154. MPEG-2 is an audio / video compression algorithm optimized for broadcast quality up to the HDTV standard based on discrete cosine transform and motion estimation. For the DVB project, we chose the main MPEG-2 profile at the main level with a maximum data transfer rate of 15 Mbps.

The basic level means that up to 720x567 pixels at 25 Hz (the television frequency standard used in Europe) or up to 720x480 pixels at 30 Hz (used in North America), the aspect ratio is supported:

• 4: 3.
• 16: 9.
• 2.21: 1.

A basic profile means that bidirectional MPEG frames are supported, but SNR scalability or resolution is not used.

In ETR 154, certain parameters were selected that should be supported by all DVB receivers.

Video:

• A frame rate of 25 Hz in movie mode and a field frequency of 50 Hz in camcorder mode.
• The aspect ratio is 4: 3 and 16: 9 (2.21: 1 is optional).
• Receivers must support pan vectors that allow the most relevant part of the 16: 9 image to be displayed on a 4: 3 display with the correct aspect ratio.
• Image resolution resolution: 720 x 576, 544 x 567, 480 x 576, 352 x 576,352 x 288.

The MPEG-2 standard also defines the ISO / IEC13818-1 multiplexing system, which allows combining multiple streams of video and audio into one. In DVB, this multiplexing method is used to enable the implementation of many different programs with a bandwidth of 38 Mbps.

Image processing

The first films were shot in academic form 4: 3. Early TV standards adopted it, maintaining compatibility with the movie. When film producers switched to a wider format (16: 9), home television also adopted this innovation for a high-quality demonstration of scenes. Recently, films began to be released in an even wider format, 2.21: 1.

If a 16: 9 image should be displayed on a home theater screen in a 4: 3 format, there are two commonly used methods for adapting the aspect ratio of an image — panning and scanning.

Pan & scan means that a DVB-T T2 C of such a system will show every part of the movie in proportion to the ratio 4: 3 = 12: 9, and the 16: 9 window of the image will be displayed with the smaller side 9. The remaining 25% of the image area will be cropped.

DVB-T ground transmission

To understand what DVB T / C is, it is necessary to consider the properties of channel terrestrial transmission systems, for example, a variable signal-to-noise ratio, depending on large-scale multipath effects and reflection from neighboring walls of the house. They attenuate certain frequencies, create an overloaded spectrum, as well as interference from nearby analogue TV channels and from far located stations in the same band.

The selected DVB-T modulation scheme has the following characteristics:

• OFDM (Orthogonal Frequency Control Multiplex). In this method, the Fourier transform is used to generate a broadcast signal with thousands of mutually orthogonal modulated QAMs. One character carries several kilobits of information. The guard interval allows echoes to pass before the receiver detects the next character - 8192 or 2048 carrier frequencies.
• Stability of modulation scheme against echo.
• Extreme multi-path propagation, which leads to much better use of the spectrum frequency at safe distances between transmitters operating at the same frequencies.

Cable system transmitter

Digital Video Broadcasting (DVB) is a set of universally recognized open TV standards. The DVB-C transmitter input is presented as a sequence of packets with a standard MPEG transport stream. Each packet consists of 288 bytes. First, it is scrambling to dissipate energy. Further, the synchronization of the package is modified. After that, it goes through the encoder. For protection, 16 bytes are added. The length of a single packet becomes 304 bytes.

To understand, DVB-T2 C S2, what it is in a transmission format, consider the operation of packets. Modified packets pass through a convolutional interleaver with a depth of 12, followed by a display unit. It converts packet bytes into two-dimensional QAM characters with I and Q components.

Then, the two high-order bits of each character are differentially encoded to eliminate the ambiguity introduced by QAM modulation. DVB-C supports various types of QAM: 16-QAM, 32-QAM, 64-QAM, 128-QAM and 256-QAM.

DVB-C Receiver

The receiver performs the opposite sequence of operations. The radio frequency signal of the base band is adjustable in level, converted with lowering it and demodulated. For the last action, carrier and time synchronization is performed. After that, the signal passes through a matched filter. In cable systems, the channel frequency response is not uniform and can be described as a linear filter. Therefore, the demodulated signal, represented as a sequence of two-dimensional symbols, is adjusted using the equalizer.

The two most significant bits of each symbol are decoded in a differential decoder. After that, the symbols from the signal are mapped to a sequence of bytes that passes through the deinterleaver. It is followed by decoding and error correction, and then descrambling. Further synchronization bytes are modified. The output signal is a standard MPEG transport stream.

Technical Parameters of C-gear

This is a DVB system used to distribute digital TV over cable networks. DVB-C uses the same channels (8, 7 or 6 MHz) that were taken to distribute the old analog TV. It is filled with a data container that can transmit uncompressed video, audio, and MPEG-2 data. In this way, digital TV channels can be distributed without the need to stop the distribution of analog television.

DVB-C applies quadrature amplitude modulation (QAM) for data. Usually 64-QAM is used, but lower level modulation schemes such as 16-QAM and 32-QAM and higher ones such as 128-QAM and 256-QAM are also suitable. Their capacity increases when applying modulation schemes of a higher level. In this case, the data will be less resistant to noise and interference.

The 8 MHz channel can carry a payload of 38.5 Mbps if 64-QAM is used. This is enough for 4-6 television programs. DVB-C is suitable for all channels with a width of 7 MHz and 8 MHz in cable networks. In Germany, only 8 MHz channels from 230 MHz to 862 MHz are usually used for DVB-C.

New standard

Modern TVs have a new television standard. However, not all customers understand the features of the DVB T2 C. What is it? It is the standard for digital signal transmission in broadband cable television systems. The standard defines the methods of the physical layer, for example, error protection, modulation and lower layer protocols necessary for data packaging.

Compared to the predecessor DVB-C, which was originally standardized in 1994, DVB-S2 offers significant advantages in terms of transmission performance, for example, spectral efficiency and operational flexibility, variable bandwidth, improved ability to adapt to dedicated channel conditions.

DVB-C2 was developed in accordance with the DVB philosophy to use modern technologies and a number of their elements that were not used in the first generation.

The family of DVB transmission systems in the second generation standards are harmonized up to DVB-C2 (DVB-S2, DVB-T2). The combined PLP and Data Slice multiplexing techniques are an example of this novelty. They ensure that the DVB-C2 not only meets the commercial and technical requirements of the European standard, but also provides an optimized solution taking into account operational flexibility and transmission efficiency.

Comparison of modifications

Differences between DVB-T, DVB-S, DVB-C and DVB-H systems. DVB stands for Digital Video Broadcasting. The system supports higher resolution and helps increase channel bandwidth.

DVB-T:

• The short form of digital video broadcasting is terrestrial.
• The transmission modulation scheme is OFDM encoded.
• Transmits uncompressed audio and video in MPEG format.
• Used data modulation schemes: QPSK, 16QAM, 64QAM.
• Uses an external RS encoder (204,188) and an internal convolutional encoder.
• Suitable internal and external interleaver.
• It uses frequency channels VHF and UHF with a bandwidth of 6 MHz, 7 MHz and 8 MHz.

DVB-S:

• The short form of digital video broadcasting is satellite.
• Uses MPEG-2 for digital compression and decompression.
• Suitable range C, as well as the frequency range Ku.
• The DBS digital receiver uses FEC methods to correct errors.
• There are special satellites launched for this purpose.
• For transmission, the polarization types LHCP and RHCP are used.
• DVB-S basically requires a smaller antenna.

DVB-C:

• The short form of digital video is broadcast cable.
• Uses MPEG-2 or MPEG-4 compression.
• Data Modulation: 16 QAM or 256QAM.
• Uses RS encoder as FEC.
• The interlace module is suitable in the circuit.
• The signal is transmitted via coaxial or fiber optic cable from service providers to subscribers.
• This format is DVB-C that you can use frequencies from 55.25 to 403.25 MHz.

DVB-H:

• A short form of digital video broadcasting is a portable device.
• Uses frequency ranges VHF, UHF and L.
• May exist with the DVB-T system.
• This is one of the standard mobile TV formats.

Upgrade ground transmission

DVB-T is a DVB standard for terrestrial video transmission. It was first applied in 1997. Since then, Australia, Europe, part of Asia, many parts of Africa and Colombia have used it in their broadcasts and television sets. DVB-T2 is the second version of this standard introduced in 2008.

Each character that makes up a name has a meaning in DVB-T2:

• DVB is the name of the consortium responsible for creating open digital TV standards.
• T-comes from the terrestrial standard, differentiating it from satellite (DVB-S), cable (DVB-C) and portable broadcasting (DVB-H).
• "2" is the second generation.

The goal of the DVB-T2 is to achieve better TV relay, since the previous DVB-T does not have enough bandwidth to allow the emission of high-resolution channels.

Comparison of the technical characteristics of DVB-T and DVB-T2.

System compatibility

All DVB transmission systems are designed for maximum compatibility. This means that they can use common blocks of circuits, for example, Reed Solomon decoder and interleaver, if one receiver supports multiple media.

A typical DVB-C cable system has 8 MHz channels, a 15% drop, defined by DVB-C. Theoretical maximum character rate of 6.96 MB.

Using a computer

Watching cable TV on your computer is now easier thanks to the creation of TV tuners for PC and TV software with DVB-T2 C. What is it? Many viewers who are versed in electronics, this is clear from a simple functioning scheme. Cable TV tuners or TV cards work just like a standard television antenna.

The equipment receives television broadcast signals that the computer reads to create direct television products. To understand what DVB-C support is, consider the basic algorithm for connecting to a PC:

• Disconnect the power cord attached to the back of the computer unit from the electrical outlet. Unscrew the screws on the left side of the PC with a screwdriver. Remove the side panel.
• Find the peripheral interface component or PCIe slot on the motherboard. Carefully insert the cable TV tuner card into the slot. Fix this position with the screw.
• Close the PC case.
• Connect the audio and video cables supplied with the DVB-C tuner to the PC.
• Connect one end of the cable to the PC tuner box and insert the other into the color connectors on the back of the computer case.
• Match the corresponding colors with multi-colored rosettes. Many are trying to figure out what a DVB-C digital tuner is. This can be clarified from the technical documentation attached to the model.
• Install drivers for the TV tuner card.
• Click the "Start" button on the PC, first right-click on "My Computer" and select "Properties", "Device Manager", and then click on "Multimedia Controller" from the list.
• Right-click and select "Install Driver".
• Insert the installation disk that came with the TV tuner, install the program, and restart the computer. Use software to watch cable TV on a PC.

Ten years ago, not all viewers knew about the DVB-C tuner. What is this, could explain the unit. Today they are starting to apply the modern TV format everywhere, which allows more channels in one multiplex. Therefore, manufacturers of modern smart TVs are interested in introducing it into their devices. Changes are complex and affect many parties. However, experts note that a full transition to T2 will occur in 2022.