Digital Video Broadcasting - Cable (DVB-C) transmission system for digital cable television, founded in February 1994 on the European standard ETS 300 429. An innovation for TV, sound, data and framing structure developed under the auspices of the European Broadcasting Union (EBU) and the European Telecommunications Standards Institute (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 TV varieties: 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 high picture quality and better bandwidth utilization than classic analog color television standards such as PAL, NTSC and SECAM.
In January 1995, the DVB project organized by the EBU published a set of standards that define a new digital video broadcastingsystem. Since 1996, DVB has been the technical basis for the implementation of digital TV transmission in the EU in many countries of the world, including Russia. The US has its own HDTV terrestrial standard which is based on MPEG-2, uses a modem and an audio encoder.
Special 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 describes the transmission of digital TV via satellite and cable. It covers system design and a modem for high bandwidth transmission, as well as several ancillary features such as teletext, electronic program guides, and conditional access. The system is an ISO MPEG-2 algorithm.
Building blocks
To understand what DVB-C is, study the elementary scheme. The block diagram of a DVB receiver consists of a cable or an antenna:
- Receiver - demodulation - error correction - additional access control and encryption module.
- MPEG demuxer.
- MPEG video decoder.
- MPEG audio data decoder.
- Interface.
- RGB/S-Video/ PAL/PAL encoder.
- A personal computer or modem, and a DVB-C that provides compatible operation.
- TV, VCR.
- Hi-Fi system.
The first generation of consumer DVB receivers consisted of a small box containing the receiver and the above MPEG decoder.
The receivers have a data transmission system, interfaces for personalcomputers and other multimedia systems (EIA-232-E), one or more ISO 7816 chip card slots, type 2 PCMCIA connectors for pay TV access control module, and a DVB-C in the TV that can provide cable connection. Additional interfaces may include digital audio.
MPEG-2 encapsulation
The DVB project has not defined its own image encoding algorithm, but has chosen a profile (subset) of the international standard ISO/IEC 13818, commonly referred to as MPEG-2 in ETR 154. MPEG-2 is an audio/video compression algorithm optimized for broadcast quality up to HDTV standard based on discrete cosine transform and motion estimation. For the DVB project, the MPEG-2 main profile was chosen at the main level with a maximum data rate of 15 Mbps.
Main level means that up to 720x567 pixels at 25Hz (TV frequency standard used in Europe) or up to 720x480 pixels at 30Hz (used in North America) aspect ratios are supported:
- 4:3.
- 16:9.
- 2, 21:1.
Main profile means that bidirectional MPEG frames are supported, but no SNR or resolution scalability is used.
Specific parameters have been chosen in ETR 154 to be supported by all DVB receivers.
Video:
- Frame rate 25Hz in film mode and field rate 50Hz in camcorder mode.
- Aspect ratio 4:3 and 16:9 (2, 21:1 optional).
- Receivers must support pan vectors,which allow the most relevant part of a 16:9 image to be displayed on a 4:3 display in the correct aspect ratio.
- Image brightness 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 multiple video and audio streams to be combined into one. In DVB, this multiplexing method is used to allow many different programs to be implemented with a bandwidth of 38 Mbps.
Image processing
The first films were shot in 4:3 academic format. Early TV standards adopted it, maintaining film compatibility. When movie producers switched to a wider format (16:9), home TV also adopted this innovation to show the quality of the scenes. Recently, films have been released in an even wider 2.21 format: 1.
If a 16:9 image is to be displayed on a 4:3 home theater screen, there are two commonly used methods to adjust the aspect ratio of the image - panning and scanning.
Pan & scan means that the DVB-T T2 C of such a system will display each part of the film in proportion to 4:3=12:9 ratios, and the 16:9 image window will be displayed with a smaller side of 9. The remaining 25% image area will be cropped.
DVB-T Terrestrial transmission
To understand what DVB T / C is, you need toconsider the properties of channel terrestrial transmission systems, for example, the variable signal-to-noise ratio, depending on the scale multipath effects and reflections from the neighboring walls of the house. They attenuate certain frequencies, create congested spectrum, as well as interference from nearby analog TV channels and from far away 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 the echo to pass before the receiver detects the next character - 8192 or 2048 carriers.
- Stability of the modulation scheme against echo.
- Extreme multipath propagation resulting in much better frequency spectrum utilization at safe distances between transmitters operating on the same frequencies.
Cable system transmitter
Digital Video Broadcasting (DVB) is a set of generally accepted open TV standards. The input signal of a DVB-C transmitter is presented as a sequence of packets with a standard MPEG transport stream. Each packet consists of 288 bytes. At first it is scrambling to dissipate energy. Next, the package synchronization is modified. After that, it passes through the encoder. 16 bytes are added for protection. Single packet length becomes 304 bytes.
To understand DVB-T2 C S2 what it is in the transmission format, consider the operation of packets. The modified packets pass through a 12-depth convolutional interleaver followed by a mapper. It converts the packet bytes into 2D QAM symbols with I and Q components.
The two most significant bits of each symbol are then differentially encoded to remove the ambiguity introduced by the 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 baseband RF signal is level-adjusted, downconverted, and demodulated. For the last action, carrier and time synchronization is performed. The signal then passes through a matched filter. In cable systems, the frequency response of a channel is not uniform and can be described as a linear filter. Therefore, the demodulated signal, represented as a sequence of two-dimensional symbols, is corrected using an equalizer.
The two most significant bits of each character are decoded in the differential decoder. The symbols from the signal are then mapped to a sequence of bytes that passes through the deinterleaver. This is followed by decoding and error correction, and then descrambling. Next, the sync bytes are modified. The output is standard MPEG transport stream.
C-transmission specifications
Thisa DVB system used to distribute digital TV over cable networks. DVB-C uses the same channels (8 MHz, 7 MHz or 6 MHz) that were used to distribute the old analog TV. It is populated with a data container that can carry uncompressed video, audio, and MPEG-2 data. In this way, digital TV channels can be distributed without having to stop the distribution of analogue TV.
DVB-C uses quadrature amplitude modulation (QAM) for data. Typically 64-QAM is used, but lower-level modulation schemes such as 16-QAM and 32-QAM and higher-level modulation schemes such as 128-QAM and 256-QAM are also suitable. Their capacity increases with the use of higher level modulation schemes. In this case, the data will be less resistant to noise and interference.
An 8 MHz channel can carry a payload of 38.5 Mbps if 64-QAM is used. This is enough for 4-6 TV programs. DVB-C is suitable for all 7 MHz and 8 MHz channels on cable networks. In Germany, DVB-C usually only uses 8 MHz channels from 230 MHz to 862 MHz.
New standard
Modern TVs have a new TV standard. However, not all buyers understand the features of DVB T2 C. What is it? It is the standard for digital signal transmission in broadband cable television systems. The standard defines the physical layer methods, such as error protection, modulation, and lower layer protocols, necessary for data packaging.
Compared toThe predecessor of DVB-C, which was originally standardized in 1994, DVB-S2 offers significant transmission performance advantages such as spectral efficiency and operational flexibility, variable bandwidth, improved ability to adapt to dedicated channel conditions.
DVB-C2 has been developed in line with the DVB philosophy to use modern technologies and a number of their elements that were not used in the first generation.
Family of DVB transmission systems in second generation standards harmonized up to DVB-C2 (DVB-S2, DVB-T2). The combined PLP and Data Slice multiplexing concept methods are an example of such novelty. They ensure that DVB-C2 not only meets the commercial and technical requirements of the European standard, but also provides an optimized solution for 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 to increase the bandwidth.
DVB-T:
- Short form of digital video broadcasting - terrestrial.
- Transmission modulation scheme - coded OFDM.
- Transmits uncompressed MPEG audio and video.
- Used data modulation schemes: QPSK, 16QAM, 64QAM.
- Uses external encoder RS (204, 188) and internal convolution.
- Inner and outer interleaver fit.
- Uses frequencyVHF and UHF channels with 6 MHz, 7 MHz and 8 MHz bandwidth.
DVB-S:
- Short form of digital video broadcasting is satellite.
- Uses MPEG-2 for digital compression and decompression.
- Suitable for C band as well as Ku band frequencies.
- The DBS digital receiver uses FEC methods for error correction.
- There are special satellites launched for this purpose.
- LHCP and RHCP polarization types are used for transmission.
- DVB-S generally requires a smaller antenna.
DVB-C:
- 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 interleaving module fits in the circuit.
- The signal is transmitted over coaxial or fiber optic cable from service providers to subscribers.
- A DVB-C format that can use frequencies from 55.25 to 403.25 MHz.
DVB-H:
- Short form of digital video broadcasting - portable device.
- Uses VHF, UHF and L band frequencies.
- May exist with DVB-T system.
- This is one of the standard mobile TV formats.
Ground transmission upgrade
DVB-T is a terrestrial video transmission standard created by DVB. It was first applied in 1997. Since then, Australia, Europe, parts of Asia, many parts of Africa and Colombia have used it in their broadcasts and television receivers. DVB-T2 isthe 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 - derived from the terrestrial standard, differentiating it from satellite (DVB-S), cable (DVB-C) and portable broadcast (DVB-H).
- "2" is the second generation.
The goal of DVB-T2 is to achieve better TV rebroadcasting, as the previous DVB-T does not have enough bandwidth to allow high definition channels to be emitted.
Comparison of technical characteristics of DVB-T and DVB-T2.
| Device, process | DVB-T | DVB-T2 |
| Input interface | TS Simple | Multiple TS and GSE |
| Modulation | OFDM | OFDM |
| Error Correction (FEC) | 1/2, 2/3, 3/4, 5/6, 7/8 | LDPC + BCH1 / 2, 3/5, 2/3, 3/4, 4/5, 5/6, 6/7, 8/9 |
| Modulation scheme | QPSK, 16QAM, 64QAM | QPSK, 16QAM, 64QAM, 256QAM |
| Guard interval | 1/4, 1/8, 1/16, 1/32 | 1/4, 19/128, 1/8, 19/256, 1/16, 1/32, 1/128 |
| FFT size | 2k, 8k | 1K, 2K, 4K, 8K, 16K, 32K |
System compatibility
All DVB transmission systems are designed for maximum compatibility. This means that they can use common circuit blocks, such as the Reed Solomon decoder and interleaver, if one receiver supports multiple transmission media.
In a typical DVB-C cable system there are 8 MHz channels, 15% roll-off defined by DVB-C. Theoretical maximum symbol rate is 6.96MB.
Using a computer
Watching cable TV on PC is now easier thanks to the creation of PC TV tuners and TV software with DVB-T2 C. What is it? For many viewers who understand electronics, this is clear from a simple operation diagram. Cable TV tuners or TV cards work just like a standard TV antenna.
The equipment accepts broadcast TV signals that are read by a computer to create a live TV production. 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 a peripheral interface component or a PCIe slot on the motherboard. Gently insert the cable TV tuner card into the slot. Secure this position with a screw.
- Closing the casePC.
- Connect the audio and video cables supplied with the DVB-C PC tuner to the PC.
- Connect one end of the cable to the PC tuner box and plug the other end into the colored connectors on the back of the computer case.
- Match matching 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 the drivers for the TV tuner card.
- Click the "Start" button on the PC by first right-clicking "My Computer" and selecting "Properties", "Device Manager" and then clicking "Media Controller" from the list.
- Right-click and select "Install Driver".
- Insert the installation disc supplied with the TV tuner, install the program and restart the computer. Use software to watch cable TV on PC.
Ten years ago, not all viewers knew about the DVB-C tuner. What it is, units could explain. Today, the modern TV format is beginning to be widely used, which allows a greater number of channels in one multiplex. Therefore, manufacturers of modern smart TVs are interested in introducing it into their devices. The changes are complex and affect many parties. However, experts note that a full transition to T2 will occur as early as 2022.
