dvb t2 signal parameters accepted for broadcasting. Broadcasting standards: DVB-T, DVB-T2, DVB-S, DVB-S2

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The article provides an overview of the main features and advantages of the digital broadcasting standard DVB television-T2. Quantitative indicators of the gain in performance of certain parameters of the new standard relative to the old version of DVB-T are given.

The article describes the main features and benefits of digital terrestrial television standard DVB-T2. Quantitative indicators of performance gain of certain parameters of the new standard with respect to the old version of DVB-T.

Keywords:

terrestrial television, signal, information.

terrestrial TV, signal, information

UDC 001.08

Modern digital technologies open up qualitatively new opportunities for society to receive and transmit information. Terrestrial television is one of the main ways of obtaining information nowadays. Terrestrial digital television, unlike other types digital television, delivers the signal to the consumer without unnecessary wires. However, the question of high-quality signal delivery to the consumer in conditions of severely limited spectrum and a large amount of interference immediately arises. It is to solve these problems that the DVB-T2 standard was developed.

DVB-T2 has several main differences from DVB-T. In particular, not only the MPEG-2 transport stream (TS), but also the generic transport stream can be used to encapsulate information. General-purpose TP uses a variable packet size, rather than a fixed one, as in MPEG-2. This allows you to reduce the amount of transmitted service data and make the adaptation of transport to the network more flexible. In addition to transport streams, any other digital streams can also be transmitted. Thus, compared to DVB-T, there is no longer any binding to any data structure at the transport level.

Further, the distribution of COFDM carriers between logical information flows, the so-called PLP (physical layer pipes) has been introduced. In DVB-T, the entire bandwidth was allocated for the transmission of one transport stream. In DVB-T2, simultaneous transmission of several transport streams is possible, each of which is placed in its own PLP. Two operating modes are possible: with the transmission of one PLP - “Mode A” and with the transmission of several PLPs - “Mode B”.

The use of such a mechanism can, in particular, reduce the power consumption of the subscriber device, since it can be turned off at the moment when PLPs that are not needed by the subscriber are transmitted.

For single-frequency networks, the MISO mode (multiple input single output - many inputs, one output) has been introduced, which allows you to achieve up to 70% gain in bandwidth. Experience in operating single-frequency networks has shown that even when synchronized signals are added, the resulting COFDM spectrum undergoes distortion (in the form of “dips” in the COFDM carrier envelope). As a result, to compensate for these “dips”, that is, to maintain the required signal-to-noise ratio, higher transmitter power is required. MISO mode allows you to avoid this trouble. The basic idea here is that transmitters on a single-frequency network in MISO mode do not emit exactly the same signal. Thanks to this, when adding signals from different transmitters, “dips” in the envelope do not arise and an increase in the power of the transmitters is not required.

Another innovation is the introduction of 256QAM modulation mode - transmitting 8 bits on a carrier. This allows you to increase the channel capacity by a third. It would seem that such a mode would lead to much more stringent requirements for the signal-to-noise ratio. However, the noise immunity of LDPC codes is so high that they can compensate for errors that arise when using 256QAM without increasing the signal-to-noise ratio.

An extended mode has been introduced for the number of carriers 8k, l6k and 32k. It lies in the fact that in the case where there are no strict requirements for compatibility with stations in an adjacent channel, additional carriers can be added from the edges of the COFDM spectrum. With an increased number of carriers, the spectrum has a steeper rolloff at the edges, and adding carriers does not cause the spectrum shape to go beyond the acceptable mask. Adding carriers allows you to gain 1...2% of channel capacity.

A multi-channel reception function was also implemented. T2 includes the optional capability to receive from two transmitters. In cases where the receiver “sees” the signal from two transmitters at once, for example, when receiving an omnidirectional antenna in a small single-frequency network, its use can significantly improve the performance of the system. This encoding, together with changing the format of the pilot signals, makes it possible to losslessly separate and separately decode signals received from two different air channels. Moreover, code overlay does not degrade reception if only one channel is available to the antenna. Preliminary calculations have shown that this technique can increase the coverage area of small single-frequency networks by up to 30%.

To protect signals, that is, each carrier used for transmission of this symbol To prevent distortion under multipath conditions, duplication of the end of each symbol in the guard interval preceding the transmission of this symbol has been introduced.

The length of the guard interval is selected depending on the estimated length of the air path and other parameters of the transmission network. Longer guard intervals are required in single-frequency networks, where signals from neighboring transmitters may arrive at the receiver with a significant delay relative to the main signal. The guard interval is an add-on that eats up a share of the transport resource. In DVB-T, this add-on can take up to 1/4 of the total amount of transmitted data. To be able to lengthen the guard interval without increasing its share in the total data volume in T2, two new modes were introduced - 16k and 32k - with a corresponding increase in the number of orthogonal carriers. That is, the absolute value of the guard interval is maintained, but its share in the total volume decreases. For example, in FFT equal to 8k, the protective premium is 25% of the symbol duration, and in 32k mode only 6% of the duration.

Thus, T2 offers a wider range of FFT dimensions and guard intervals. Namely:

FFT dimensions: 1k, 2k, 4k, 8k, 16k, 32k;

Relative duration of guard intervals: 1/128, 1/32, 1/16, 19/256, 1/8, 19/128, 1/4.

The maximum duration of the guard interval in T2 is achieved in the 32k mode with the ratio of the guard premium and the length of the entire symbol being 19/128. The duration of the protective surcharge exceeds 500 μs, which is quite enough to build a large nationwide single-frequency network.

As the number of carriers increases in the same frequency band, the probability of intersymbol interference increases. In order for it not to be too large, it is necessary to increase the duration of the modulation symbol accordingly. It would seem that this will not allow increasing the data transfer rate: simultaneously with the increase in pure carriers, their transmission time also increases. However, the requirements for the absolute duration of the guard interval do not change, since the arrival time of the reflected signal does not depend in any way on the duration of the symbol. A guard interval of 1/128 in 32k mode will have the same absolute duration t=28 µs as 1/32 in 8k mode, and therefore provide exactly the same protection against reflected signals. The use of new guard intervals together with new values of the fast Fourier transform allows us to obtain a gain of 2... 17% of the channel capacity and increase the distance between stations.

Channel coding in DVB-T used convolutional codes in conjunction with Reed-Solomon codes. DVB-T2 proposes the use of more efficient LDPC codes instead of convolutional codes and BCH codes instead of Reed-Solomon codes.

Low-density parity-check code (LDPC - Low-density parity-check code) is a code used in information transmission, a special case of a block linear code with a parity check. A special feature is low density significant elements check matrix, due to which the relative simplicity of the implementation of coding tools is achieved.

Bose-Chaudhury-Hocquengham (BCH) codes constitute one of the large classes of linear error-correcting codes. Moreover, the method for constructing these codes is specified explicitly. To further reduce the error rate, an external VCH code protection level is used, which operates at a low error density. In most modes the code can correct up to 12 errors, but in some modes it can correct up to 8 or 10 errors.

The effectiveness of these codes has been known for a long time, but previously it was not possible to

create a cheap implementation based on microelectronics. Test simulation of LDPC-based noise protection showed a significant increase in noise immunity compared to the protection used in DVB-T, that is, convolutional coding in combination with the Reed-Solomon code. The gain in C/N level due to the new FEC can be up to 3 dB for a typical error level and with the same share of control symbols. Essentially, this improvement allows you to increase throughput channel by approximately 30%, for example, due to the use of more high level constellations.

Changes are also made to the interleaving scheme. Practical use of DVB-T showed insufficiently good resistance to impulse noise. Particularly in an urban environment, using 64QAM with low FEC (Forward Error Correction) values may be more effective than using 16QAM with high FEC values.

T2 uses three stages of interleaving. This practically guarantees that distorted elements, including those caused by burst errors, will be scattered throughout the LDPC FEC frame after deinterleaving in the decoder. This should allow the LDPC encoder to perform the recovery.

We list these cascades:

1) bit interleaver: randomizes the bits within the FEC block;

2) time interleaver: redistributes the FEC block data across symbols within the T2 frame. This increases the signal's resistance to impulse noise and changes in the characteristics of the transmission path;

3) frequency interleaver: it randomizes the data within an OFDM symbol in order to reduce the effect of frequency selective fading.

To counter impulse interference, DVB-T2 additionally introduces temporary interleaving, that is various components information is interspersed along the time axis with a period of about 70 ms. That is, the data, before being transmitted over the communication channel, is rearranged in a given order, and in the receiving part the original order is restored, i.e. deinterleaving is performed. In this case, a packet error that occurs in a communication channel turns into a set of single errors dispersed in time, which are easier to detect and correct using error-correcting codes. Thanks to this, information lost in one period of time can be restored using information transmitted in another period of time.

In DVB-T, interleaving was carried out only within one modulation symbol, and therefore only during the transmission time of this symbol. If information was lost at some point in time due to interference in the communication channel, it could not be restored based on information transmitted at another point in time.

In DVB-T2, the interleaving system is more complicated; time interleaving is introduced, which makes it possible to increase the resistance of transmission to impulse noise, which is so characteristic of large cities. That is, information is interleaved not only within one modulation symbol, but also within one superframe. Of course, this requires the subscriber device to have a large RAM, where during de-interleaving it will be necessary to store a temporary interleaving block, or T1 block, and not one character, as in DVB-T. DVB-T2 introduces two new structures that are “responsible” for interleaving - an interleaving frame and a temporary interleaving block (T1 block). Essentially, these structures define the boundaries within which interleaving will take place.

An interleaving frame consists of an integer number of T1 blocks. This number can be changed. However, it is recommended to use a combination of one interleaving frame and one T1 block, since it is in this case that the interleaving will take longer to complete. long period time. The number of FEC blocks in one T1 block may not be constant. Each interleaving frame is projected onto one or more T2 frames.

Some of the carriers, the so-called pilot carriers, or synchronization markers are used to synchronize the clock frequencies of the modulator and demodulator, synchronize the spectrum carrier frequencies, frame synchronization, estimate the channel state and the level of phase noise. There are continuous (continuous) pilot signals, transmitted on the same carrier, and distributed (scattered), transmitted on several carriers, evenly distributed in the signal spectrum and varying from symbol to symbol. The pilot carriers are modulated by a specially generated pseudo random sequence. To improve noise immunity, they are transmitted at a level 16/9 times (approximately 2.5 dB) higher than other carriers.

OFDM systems use distributed pilot signals. They are modulated elements, spaced in a certain way across carriers and in time. The receiver knows the modulation parameters of the pilot signals and can use them to estimate the channel state. In DVB-T, every twelfth modulated element is a pilot signal, that is, they occupy 8% of the total data volume. This proportion is used for all guard interval options, and the placement of the pilot signals should be such as to allow the signals to be aligned with the 1/4 guard interval. However, for smaller guard intervals, the addition of pilot signals in the amount of 8% turns out to be excessive. DVB-T2 defines eight in various ways placement - PP1...8 (PP - pilot pattern). Each variant of the relative duration of the guard interval corresponds to several possible options for placing pilot signals. They are dynamically selected depending on the current state of the channel, which allows optimizing their number. Choosing the optimal method allows you to reduce the amount of transmitted service information by 1...2%.

Denser pilot placement can be used to reduce the required C/N level at the receiver input or to improve synchronization. In the latter case, the pilot signals are modulated with a pseudo-random sequence.

Another interesting innovation is rotating constellations. After the COFDM signal is generated, the constellation is “rotated” in the complex plane. To demonstrate the principle, this diagram can be simplified for only four points of the complex constellation plane, that is, for the QPSK mode as shown in Figure 2.6. The modulation symbol is rotated in the complex plane by a certain angle, depending on the number of modulation levels (29° for QPSK, 16.8° for 16-QAM, 8.6° for 64-QAM and arctg (1/16) for 256-QAM ). Moreover, before the rotation begins, the quadrature Q coordinate of each modulation symbol is cyclically shifted within one codeword, i.e. is taken from the previous character of this word, the Q-component of the first character becomes equal to the Q-component of the last.

The use of rotating constellations can provide a gain of up to 7.6 dB in signal-to-noise ratio.

A significant portion of transmission costs is the cost of the electricity that powers the transmitters. OFDM signals are characterized by a relatively high peak-to-average power ratio. In this regard, T2 includes two technologies that can reduce this ratio by approximately 20%. And this, in turn, significantly reduces power costs.

To reduce the peak-to-average power ratio (PAPR), two methods are proposed - ACE (Active Constellation Extension) and TR (Tone Reservation). The lower the RAPR value, the higher the power efficiency of the transmitter. Both methods can be used simultaneously, however, the first is preferable for constellations with a smaller number of vectors (QPSK), the second - with a larger number (QAM). Each method also has its drawbacks. The use of ACE will lead to a decrease in the signal-to-noise ratio at the input of the receiving device, and the use of TR will cause a decrease in channel capacity, since it involves the use of part of the carriers for transmitting special correction signals.

The T2 specification includes two additional tools that can be used to expand the frame in the future. Firstly, the T2 frame structure provides for the possibility of introducing signaling for as yet non-existent frame types that will be dedicated to as yet undefined signal types

That is, the content of these FEF (Future Extension Frames) frames is not yet defined, but only the header structure is defined. Including appropriate signaling in the T2 specification will allow first generation receivers to recognize and ignore FEF fragments. But the space reserved today will ensure that the first transmission systems are backward compatible with future ones in which this signaling will carry information about new types of content.

T2 also includes signaling required for future implementation of Time Frequency Slicing (TFS). Although the basic specification is for non-TFS reception, the signaling includes markings that will allow future dual-tuner receivers to handle TFS signals. Such a signal will occupy several radio frequency channels, and different parts of each service will generally be transmitted on different frequencies. The receiver will jump from channel to channel, collecting fragments of data related to the service being received. This will make it possible to form packets with sizes significantly larger than those allowed for one radio frequency channel, which, in turn, will provide the opportunity to benefit from statistical multiplexing of a significant number of channels and flexibility in frequency planning.

Comparing the main parameters when transmitting signals in the DVB-T and DVB-T2 standards, we can say that resistance to interference, picture quality, signal transmission speed and other indicators of the signal in DVB standard-T2 is about 1.48 times better than DVB-T. Also an undeniable advantage The new standard is that the capacity of digital television networks increases by at least 30% with the same network infrastructure and frequency resources.

Bibliography:

1 Lokshin B.A. Digital broadcasting: from studio to TV viewer. M.: Cyrus System Company, 2001.
2 Nick Wells, Chris Knox. DVB-T2: New broadcast standard for television high definition// Tele-Sputnik. 2008. No. 11.
3 Serov A.V. Terrestrial digital television DVB-T/N. SPb.: BHV-Petersburg. 2010.
4 Shakhnovich I. DVB-T2 new standard digital television broadcasting// Communications and telecommunications. 2009. No. 6.
5 Walter Fischer. Digital video and audio broadcasting technology. A practical engineering guide. Springer. 2010.

Reviews:

2.12.2013, 21:18 Nazarova Olga Petrovna
Review: Analysis according to standards is presented. Recommended for printing.

The new digital television standard DVB-T2 provides simple answers to questions that concern residents of the region.

What is DVB-T2?

This is the second generation of the European standard for terrestrial digital television. It differs significantly from the first generation DVB-T in physical characteristics. It is for this reason that set-top boxes and televisions with a DVB-T receiver are incompatible with DVB-T2. The second generation standard is used in a number of countries of the European Union, Ukraine, Belarus, Kyrgyzstan, Tajikistan and Armenia.

In Russia, DVB-T2 has been chosen as the digital standard terrestrial television within the framework of the Federal target program"Development of television and radio broadcasting in Russian Federation for 2009–2015." FSUE "Russian Television and Radio Broadcasting Network", the program executor, has formed two free packages(multiplex) of two dozen channels.

How does the new digital terrestrial television standard differ from the old one?

Due to the capabilities of modern equipment and more complex mathematical signal processing in the new standard, the capacity of broadcasting networks increases significantly, allowing the transmission more information in a digital package. The standard provides prospects for organizing “local” broadcasting. The DVB-T2 stream is better protected from interference. If the frequency resource is freed up, it becomes possible to receive more channels in high and ultra-high definition modes and even watch 3D television.

In addition, already now, when broadcasting the first and second multiplexes, TV viewers have access to new service: "TV Guide". In general, DVB-T2 TV is more suitable for implementing SMART functions.

Why are these changes needed at all if I was happy with everything before?

Firstly, to be confident in the future. Digital television has already replaced analog television almost all over the world. The DVB-T2 standard was chosen as the main one for use in Russia at the highest federal level, which means that in the future all television broadcasting will be carried out on its basis.

In addition, modern life directly depends on information flows, and do not ignore the data transmission capabilities provided by the DVB-T2 standard. If previously a TV was just a means for watching several TV channels, today it already combines a lot of functions, from recording missed programs to working with the Internet.

In the end, despite the fact that analogue broadcasting of channels is still fully available, the final transition to digital television is only a matter of time. It is too expensive to maintain outdated analogue television broadcasting technologies, but new technologies provide many opportunities to improve the quality of life of Russians.

Who is affected by the transition to the new standard? DVB-T broadcasting 2 ?

The changes affected exclusively those residents of the region who were already digital television subscribers and used equipment of the previous DVB-T standard. Set-top boxes, televisions with built-in decoders and DVB-T computer TV tuners are incompatible with the new standard, and broadcasting of multiplexes in the old standard in the Kaliningrad region has been stopped since mid-January.

However, according to statistics, the majority of residents of the region today use cable or satellite television, as well as IP-TV. These subscribers were not affected by the transition to the new standard. Only cable network subscribers could observe rare interruptions in the broadcast of individual programs for several days.

What equipment is required to watch channels in the new standard?

First, you will need an antenna - either a common one on the roof, or your own indoor one.

It is very likely that your TV already supports digital television standards adopted in Russia (DVB-T2 standard, MPEG-4 compression, Multiple PLP mode). Most of the world's leading manufacturers supply such TVs to our country. If you are just going to buy new TV, be sure to make sure it supports these standards.

If for some reason your TV is not compatible with digital television standards, then you will need to purchase a set-top box to receive a digital signal. It may also be called a digital terrestrial receiver or SetTopBox (STB). The standard of the set-top box is usually written on its front, make sure that the set-top box supports the DVB-T2 standard.

If you want to receive a digital television signal and cable TV channels at the same time, then you will need a so-called TV signal combiner.
It is important to know that your satellite dish does not allow you to use digital television broadcasting, as it operates in a completely different standard. In addition, it should be noted that one set-top box does not allow you to watch different digital television channels on different TVs.

Is the new broadcast standard expensive?

No, now DVB-T2 TVs and set-top boxes are no more expensive than the old standard equipment. In addition, remember - federal multiplexes are guaranteed free for the Russian population, unlike cable, satellite or Internet television. The cost of the necessary set-top box starts from 1300 rubles.

How to set up a TV to receive a signal in the DVB-T2 standard?

First of all, you should read the instructions for your TV and/or digital set-top box to connect the equipment. You may also need to activate the digital tuner of your TV (by selecting the country in the corresponding section of the settings menu - Poland, Lithuania or Germany). Then you should start an automatic channel search - in most cases, the built-in signal level and quality indicator will allow you to optimally configure your antenna for receiving digital television.

If you need manual setting digital TV channels, then use following settings: the first multiplex is broadcast on 47 TVK, frequency 682 MHz, the second multiplex - on 30 TVK, frequency 546 MHz (RTPS Kaliningrad).

What channels can you watch in the DVB-T2 standard?

Currently, two multiplexes (packages) are broadcast in the Kaliningrad region: RTRS-1 and RTRS-2.

The first multiplex, broadcast simultaneously from five transmitting stations at a frequency of 682 MHz, includes the channels: “Channel One”, “Russia” (Russia-1), “Russia-2” (Russia-2, sports channel), “NTV” , “Petersburg - Channel 5”, “Russia - Culture” (Russia-K), “Russia-24” (Russia-24), “Carousel”, “Public Television of Russia”, “TV Center”.

The second multiplex, broadcast from a transmitting station in Kaliningrad at a frequency of 546 MHz, includes the channels: “Ren-TV”, “Spas”, “STS”, “Domashny”, “TV3”, “NTV Plus Sport”, “Zvezda”, “ Mir", "TNT", "Muz TV".

Today, DVB-T2 can most likely be called the most advanced terrestrial digital television system in the world. In this article we will try to figure out how the DVB-T2 standard managed to take a leading position in the global terrestrial market. digital television broadcasting, as well as what advantages it has compared to its predecessor - the DVB-T standard.

What is DVB-T2?

The DVB-T2 standard is the most advanced digital terrestrial television (DTT) system in the world. It is characterized by greater stability, flexibility and at least 50% greater efficiency compared to all other DTT systems. This standard supports broadcasting in SD, HD, Ultra HD formats, mobile television broadcasting, as well as any combination of the above formats.

Origins

At one time, the DVB-T standard became the most widely used in the world. Since 1997, when it was officially approved as valid, more than 70 countries around the world have launched broadcasting DVB-T platforms, and today 70 countries around the world have already begun launching multiplexes in the DVB-T2 system or have officially approved this standard.

As European countries transition from analogue to digital broadcasting and the frequency spectrum shortage grows, the DVB concern outlined general commercial requirements for developers of an updated version of the standard, which was supposed to provide even more efficient use frequency resource. The DVB-T2 system was able to special problems satisfy all these requirements, including increased capacity, reliability and possibility further use existing antennas. The first version of the DVB-T2 standard was approved in 2009 (version EN 302 755), and in 2011 an improved version of the system appeared, which, in particular, includes a new substandard T2-Lite, designed for the needs of mobile broadcasting and TV reception. signal to portable devices.

How it works?

The DVB-T2 standard, like its predecessor, uses OFDM (orthogonal frequency division multiplexing) modulation with multiple subcarriers capable of transmitting a stable signal, and also has a large number of different modes, making this standard extremely flexible. The DVB-T2 system uses the same type of error correction coding that is used in the DVB-S2 and DVB-C2 systems: it is a combination of LDPC (Low Density Parity Check) and BCH (Bose-Chaudhury-Hocquengham code) coding types. ), providing high signal stability. At the same time, the system allows you to change the number of carriers, the size of guard intervals and pilot signals, making it possible to optimize the overhead for any specific transmitted channel.

The DVB-T2 system also uses additional new technologies, in particular:

Using multiple channels physical level allows you to separately adjust the stability of each of the transmitted programs within the channel to adjust to the required reception conditions (for example, an indoor antenna or an external antenna). Besides, this function allows the receiver to save energy by decoding only specific program from the multiplex, and not the entire transmitted packet.
Alamauti coding, which is a transmitter diversity method. Allows you to improve the quality of coverage in small single-frequency networks.
Constellation Rotation feature provides reliability when using low order constellations.
Extended interval function, including bit, time, square and frequency intervals.
Future Extensibility Function (FEF) - allows future enhancements to the standard while maintaining compatibility.

As a result, a DVB-T2 system can offer much higher data rates than DVB-T and also provide greater signal stability. For comparison, the bottom two rows in the table show the maximum data rates at a fixed signal-to-noise ratio and the required signal-to-noise ratio at a fixed (usable) data rate.

T2-Lite

The T2-Lite subsystem was the first additional profile in the standard that was added due to the existence of the FEF principle. This profile was officially introduced in July 2011 to support mobile broadcasting and reception on portable devices, as well as reducing the costs of implementing these types of broadcasts. The new profile is a subsystem of the DVB-T2 standard using two additional LDPC encoding rates. By using only elements relevant to reception on mobile and portable devices in the subsystem, as well as limiting the data transfer rate to 4 Mbit/s per physical layer channel, the complexity of creating and implementing a new chipset was reduced by 50%. The use of FEF principles allows programs to be transmitted in the same frequency channel in T2-Lite and basic T2, even when the two profiles have different indicators Quick conversion Fourier transform (FFT) or various guard intervals.

Conquering the market

As with DVB-T, the new standard was intended not only for transmitting programs to devices equipped with external or indoor antennas, but also for reception on PCs, laptops, car TVs, radios, smartphones, dongles, and other innovative receivers . In countries where DVB-T platforms were already in operation, the DVB-T and DVB-T2 standards usually continue to coexist for some time, and in those countries where there was no digital broadcasting as such, there is a unique opportunity to switch directly from analogue to digital broadcasting to the DVB-T2 standard, bypassing the DVB-T implementation stage.
Currently, there are a huge number of DVB-T2-compatible set-top boxes and televisions on sale on the world market, and prices have already dropped to $25 for the cheapest models. The price difference between DVB-T and DVB-T2 compatible TVs is no longer significant.
The first country to begin introducing digital broadcasting in the DVB-T2 standard was Great Britain, where DVB-T2 broadcasting was launched in March 2010 in parallel with existing DVB-T platforms. During 2010-2011, DVB-T2 platforms were launched in Italy, Sweden and Finland, and very soon in each of these countries broadcasting in this standard was organized at the national level.
In Ukraine, the launch of on-air digital broadcasting in the DVB-T2 format began in the fall of 2011. The construction of a network of on-air transmitters was carried out by the Zeonbud company. In January 2012, the air digit signal was encoded by the Irdeto Cloaked CA conditional access system. In this regard, the market for receiving equipment was limited, and as a result of tenders held in April and July 2012, two companies became the main suppliers of digital set-top boxes - Strong and Romsat.
However, in July of this year, the National Council for Television and Radio Broadcasting, in its new composition, turned the country’s digitalization process 180 degrees, obliging the provider of the national digital broadcasting network Zeonbud to disable signal encoding. Thus, the introduction of the DVB-T2 standard on the territory of Ukraine takes on a new color, and, most likely, in the near future the television market will be overflowing with digital television receivers at an affordable price, which will actually stimulate the population’s interest in the new type of television, and will also allow the country to fulfill its The deadline for commitments to switch to digital is July 17, 2015.
Note that paid DVB-T2 platforms have also been launched outside Europe. For example, in Zambia, Namibia, Nigeria, Kenya and Uganda, and in a number of other countries, the launch of broadcasting in this standard is expected in the very near future. Test broadcasts of this standard are currently being carried out in many parts of the world, and many countries are considering adopting DVB-T2 as a digital terrestrial broadcasting standard.

Surely many Russian users interested in terrestrial television have already heard about the gradual transition to digital broadcasting throughout the country. Many TV viewers have no idea what needs to be done to switch to digital TV, whether they need to purchase additional equipment or not. In this material, I will try to answer all the questions of users planning to use digital TV on their TVs, because the digital television standard, thanks to information technology, is being transformed into a new service for the viewer.

Advantages of digital TV and disadvantages of analogue

The main disadvantage of the analog signal is poor protection against interference, as well as a fairly wide band of the radio frequency spectrum required for broadcasting one channel. Therefore, on the air we were limited to a maximum of two dozen color channels, and on cable networks an average of 70. With an analog signal, it is quite difficult to create a service convenient for the user and operator (for example, to implement the ability quick connection and disabling channel packages). In addition, analog TV requires high power transmitters with a large coverage area.

A digital signal does not have these disadvantages. The main advantage of digital TV is that the signal can be compressed using modern algorithms (for example, MPEG). By compressing the signal in the frequency range of one analog television channel, you can fit up to 10 digital channels with approximately the same picture quality. Exactly how to encode and compress a signal is determined by a single standard. Today in Europe and Russia the main family of standards is DVB - a product of the international consortium DVB Project. The family includes standards for satellite, terrestrial, cable and mobile television, differing in the degree of compression, noise immunity and other parameters (depending on the transmission medium used).

Advantages of digital TV

noise immunity, compression capability;
improving picture quality (digital signal is less sensitive to interference than analog);
a larger number of over-the-air channels compared to analogue broadcasting.

World digital TV standards

In America, the ATSC standard, developed by the Advanced Television Systems Committee group, is widespread, in Japan ISDB (Integrated Services Digital Broadcasting) is rapidly developing, Russia has followed the European path, adopting the DVB (Digital Video Broadcasting) standard as a basis.

Let's go digital

A massive transition to digital television broadcasting standards in the world took place in the early 2000s. In our country, government broadcast channels began the transition to digital in 2009 as part of the federal program “Development of television and radio broadcasting in the Russian Federation for 2009-2015.” DVB-T2 was chosen as a unified digital broadcasting standard, which allows more digital channels to be placed on the frequency band than its predecessor DVB-T, but this does not mean an increase in the resolution of the broadcast picture. We should expect HD quality on air only in the distant future. Today, DVB-T2 transmitters operate almost throughout the country. In some places, only the first multiplex (package of 10 digital channels) is currently on; in other areas, the second is already available. This means that if you have an appropriate TV or an additional set-top box, you can receive and watch 20 channels for free in decent quality and almost without interference. The program for the development of digital television in Russia involves updating only distribution and transmission equipment. Viewers have to think about replacing receivers on their own, because to receive a digital terrestrial television signal you need DVB-T2 TV tuner, and a similar one is provided only in . To receive a signal with older devices, TV viewers will have to purchase and install a set-top box at home.

Video compression formats in the DVB standard

DVB standard- is not Full description digital television format, but a method for a specific broadcast implementation. Various video encoding systems can be used within this standard (MPEG-1, MPEG-2, MPEG-4, etc.), but not all of them are backward compatible. The most common compression formats are MPEG-2 ( best quality pictures) and MPEG-4 (has better compression). Russian digital TV will use MPEG-4 compression. TVs that support the MPEG-4 standard can also work with MPEG-2, but not vice versa, since MPEG-2, in turn, is used by cable operators who are not limited in frequency band and the picture compressed with this codec is much higher quality.

Analog antenna or satellite dish?

The principle of operation from a satellite dish. You need to buy and install a set of signal receiving equipment: a dish, an access card satellite channels and a set-top box (satellite receiver), which ensures the transformation of the received digital signal into an analogue one that is understandable to the TV. Satellite receiver - this is a device that provides transformation of a signal from DVB (various decoding systems) into a format perceived by a household TV. You can connect a cable operator’s wire or a familiar terrestrial television antenna to such a set-top box. Intermediate equipment may not be needed, since many modern TVs support the standard DVB-T, which means it is compatible with MPEG-4 compression and does not require a special antenna to receive the digital signal.

In order not to change the TV, there is an alternative - CAM module. It is a kind of expansion card that is inserted into the TV and gives it the functionality of a set-top box, but to use this component the TV must have a CAM interface. I will tell you more about the CAM module in the section on digital cable TV.

Satellite platforms officially operating in Russia use DVB-S standards and DVB-S2. Correct reception is required installed antenna(the diameter of which depends on the geographical location of the subscriber and the selected satellite), a receiver with with a valid card access and TV.

DVB-T2 - a new standard for digital television

DVB-T2 standard- This is the second generation of the European terrestrial digital broadcasting standard DVB-T. It is designed to improve the capacity of television networks by at least 30% compared to DVB-T with the same network infrastructure and frequency resources.

Advantages of the DVB-T2 standard:

increasing the number of channels in the broadcast package;
the possibility of organizing “local” broadcasting;
the possibility of developing high-definition television;
release of ethereal frequencies.

The use of the DVB-T2 standard in subscriber devices creates a technological basis for the provision of digital terrestrial television broadcasting through networks additional services and HDTV. In the future it is possible to introduce a new interactive technology, thanks to which the capabilities of a conventional TV will become an analogue of Smart TV. So when buying a TV, pay attention to support for the DVB-T2 standard.

Image resolution in digital television

Ordinary television signal has "standard definition" ( Standard Definition,SD), there is also an improved quality signal option ( "increased clarity") - 480p, 576p, 480i or 576i. The number indicates the number of pixels in height, and the letter indicates the scan type - interlaced (i) or progressive (p). The number of pixels in width depends on the aspect ratio of the picture, which leads to the existence of several more types of high-definition signal. There are at least four SD options in modern analog TV. If your TV has DVB-T support, there will be no compatibility problems. Cable and satellite operators, as a rule, offer one or another version of the “high-definition” image. IN currently The DVB-T standard is considered obsolete and has been replaced by DVB-T2. In Russia, digital broadcasting is carried out in DVB-T2 standard with support for MPEG4 video compression standard and Multiple PLP mode.

High Definition TV (HDTV) – best quality at this moment. HDTV comes in two flavors - 1080i and 720p. The 720p format has a resolution of 1280x720 pixels and progressive scan, and the 1080i format has an image resolution of 1920x1080 pixels with interlaced scanning. Formally, the number of pixels in a 720p image is two times less than in 1080i, but in 720p a whole frame is formed in one pass, and in 1080i half. 1080i is more suitable for video with a minimum of movement and maximum detail, while 720p is the opposite, for this reason there is no need to compare them.

Digital cable television

In parallel with the transformation of terrestrial television, cable operators are also thinking about optimizing the frequency spectrum and developing services. In the field cable television A typical development path is the launch of broadcasting in the DVB-C format (a version of the DVB standard for cable networks, characterized by a lower compression ratio and less noise immunity compared to the terrestrial standard, which is quite acceptable in cable). When switching to digital, operators have the opportunity to flexibly manage content, for example, allocating channel packages, opening and closing access to them for users, etc. To decrypt encrypted channels on the subscriber’s side, so-called access cards are used. Each encoding system has its own, but the standard provides a universal connector for connecting a CAM module to a TV or set-top box for a specific type of encoding, into which an access card is already installed.

Like DVB-T2, the cable version of digital TV supports high-definition content (HD). But it is up to each operator to decide whether or not to include HD channels on their network. It should be noted that almost all cable networks in Russia, where digital television has been launched, offer HD channels. Some even experimented with 3D channels.

Equipment for receiving DVB-T2 and DVB-C

To view a digital signal from cable networks, you need equipment that accepts the appropriate standard. TVs and set-top boxes with DVB-C support went on sale back in 2007, so if you have changed your TV receiver in the last few years, then you most likely have support for the cable version of the DVB standard. Ideally, to connect to cable digital television, the owner of such a TV only needs to purchase a CAM module from the operator and install an access card there. But since each operator itself determines the policy for the operation of the service, CAM modules are sometimes not offered, and then subscribers need to purchase an intermediary device - a set-top box with support for the conditional access system (CAS) used by the operator. Most often, such devices are “tailored” for only one VAT.

If cable operator offers HD channels, the equipment must also accept HD resolution to view them. In general DVB-C support(DVB-T/T2) does not at all mean Full HD support (picture resolution 1920x1080 pixels for both TVs and set-top boxes). The situation is similar with 3D channels.

The fact that a TV supports the cable version of the DVB standard does not mean that it also decodes the over-the-air digital version. Deliveries of equipment with DVB-T2 support to our country began only in 2012. So we can say with confidence that if your TV was purchased earlier, then it will not “understand” the DVB-T2 standard. Cable set-top boxes also rarely accept DVB-T2. If your TV device does not allow you to receive terrestrial “digital” by default, you do not have to change it. You can limit yourself to purchasing a set-top box for DVB-T2. Digital TV tuners of this standard Available in various designs, including compact accessories for tablets and computers with a USB connector.

Television over the Internet

An Internet channel is also used to transmit a digital television signal between the telecom operator and the viewer’s TV. Globally, network television projects can be divided into IPTV and OTT. Although OTT is a type of IPTV, they are usually considered as different services. It is generally accepted that IPTV is a service within the operator’s network that provides broadcast of channels in real time, and OTT (Over The Top) is any video service (not only broadcast of channels, but also cinema, that is, video on demand) provided via the Internet . Many common operator platforms support both options within the same service, so it makes no sense to talk about a strict separation of IPTV and OTT.

Equipment for IPTV or OTT

At the moment, TV manufacturers have not yet agreed on a single standard for IPTV (OTT) services. Therefore, while viewers are forced to choose between several available options watching TV over the Internet:

– operators provide applications to connect to the service. It is important that you cannot use a third-party solution here: the only one who can release such a program for this particular network is the operator providing the service.
– the ability to connect IPTV to a TV is determined by the presence of connectors for connecting a set-top box. The cost of such devices, however, is slightly higher than that of broadcast consoles. There are even universal devices that work in networks different operators(reconnection may require changing the gadget's firmware, but at least not purchasing new equipment), as well as those acting as a home media center (for example, Dune HD).
watching channels on a computer – Often the “computer” package is smaller and you can rarely find HD channels there.
television on mobile devices.

Note that IPTV can broadcast HD, 3D and even channels. But to view them you need a set-top box and TV that support these standards and resolutions.

TV on mobile devices

The idea of mobile television has become widespread when high-speed mobile Internet and IPTV are combined. Its advantage compared to terrestrial, cable and satellite digital standards is that potentially a television signal can be received not only on specially produced devices, but also using any mobile device, including a smartphone or tablet. This is what many telecom operators who have previously launched IPTV (OTT) projects take advantage of. To work with encoded content, telecom operators release applications for mobile gadgets. Moreover, such programs often allow you to manage subscriptions to channels or a home set-top box. Recently, many projects have appeared that are not associated with any telecom operator or provider at all, but only offer video content for smartphone users, such as Amediateka, free IVI, etc.

I hope you now understand the differences between the types of digital TV: cable, Internet television, satellite and terrestrial.

(Korean Mobile TV)

T-DMB (ethereal) S-DMB (satellite) MediaFLO Codecs Video codecs

H.264 (MPEG-4 AVC)

Audio codecs Frequency range

DVB-T2 is the last in the family of DVB standards for digital terrestrial (terrestrial) television, since it is physically impossible to implement a higher “information transmission rate per spectrum unit”.

Standard

The following characteristics have been developed for the DVB-T2 standard:

COFDM modulation with QPSK, 16-QAM, 64-QAM or 256-QAM groups.
OFDM modes 1k, 2k, 4k, 8k, 16k and 32k. The symbol length for 32k mode is about 4ms.
Relative lengths of guard intervals: 1/128, 1/32, 1/16, 19/256, 1/8, 19/128 and 1/4. (For 32k mode maximum 1/8)
FEC with cascade application of LDPC and BCH correction codes.
DVB-T2 supports channel frequency bands: 1.7, 5, 6, 7, 8 and 10 MHz. Moreover, 1.7 MHz is intended for mobile television
transmission in MISO mode Multiple-Input Single-Output) using the Alamouti scheme, that is, the receiver processes the signal from two transmitting antennas

Comparison of DVB-T and DVB-T2

The following table shows the comparison available modes in DVB-T and DVB-T2.

	DVB-T	DVB-T2
Error Correction (FEC)	Convolutional code + Reed - Solomon code 1/2, 2/3, 3/4, 5/6, 7/8	LDPC + BCH 1/2, 3/5 , 2/3, 3/4, 4/5 , 5/6
Modulation Modes	QPSK, 16QAM, 64QAM	QPSK, 16QAM, 64QAM, 256QAM
Guard interval	1/4, 1/8, 1/16, 1/32	1/4, 19/256 , 1/8, 19/128 , 1/16, 1/32, 1/128
DFT dimension	2k, 8k	1k, 2k, 4k, 8k, 16k, 32k
Dispersed pilots	8% of the total	1 % , 2 % , 4 % , 8% of the total
Continuous pilots	2.6% of the total	0,35 % of the total
Bandwidth	6; 7; 8 MHz	1.7; 5; 6; 7; 8; 10 MHz
Max. data transfer rate (at SNR 20 dB)	31.7 Mbps	45.5 Mbit/s
Required SNR (for 24 Mbps)	16.7 dB	10.8 dB

Maximum data rate at 8 MHz bandwidth, 32K subcarriers, with 1/128 guard interval, PP7 subcarrier layout:

Modulation	Code speed	Maximum digital speed stream, Mbit/s	T2 frame length, OFDM symbols	Number of codes words in frame
QPSK	1/2	7.4442731	62	52
	3/5	8.9457325
	2/3	9.9541201
	3/4	11.197922
	4/5	11.948651
	5/6	12.456553
16-QAM	1/2	15.037432	60	101
	3/5	18.07038
	2/3	20.107323
	3/4	22.619802
	4/5	24.136276
	5/6	25.162236
64-QAM	1/2	22.481705	46	116
	3/5	27.016112
	2/3	30.061443
	3/4	33.817724
	4/5	36.084927
	5/6	37.618789
256-QAM	1/2	30.074863	68	229
	3/5	36.140759
	2/3	40.214645
	3/4	45.239604
	4/5	48.272552
	5/6	50.324472

DVB-T2 system structure

Generalized scheme for processing transmitted signals in the DVB-T2 system.

Service capabilities

The DVB-T2 standard allows you to provide various digital services:

3D television in the DVB 3D-TV standard;
interactive hybrid television in the Hbb TV standard;
multisound (choice of broadcast language);
access to government services in electronic form (in Russia);
emergency warning system (in Russia).

DVB-T2 signal reception

Reception of the DVB-T2 signal is carried out by an over-the-air collective, individual or indoor antenna connected to a TV with a built-in DVB-T2 tuner (decoder) or to a DVB-T2 receiver (set-top box).

Also, the DVB-T2 signal can be received on any computer with a built-in DVB-T2 digital TV tuner.

Usage

Europe

UK: one multiplex, trial run December 2009, fully operational April 2010.
Italy: one multiplex, trial run October 2010.
Sweden: two multiplexes, full launch in November 2010.
Finland: five multiplexes, trial launch in January 2011, fully launched in February 2011.
Spain: two multiplexes, full launch in 2010.

Russia

By Order of the Government of the Russian Federation dated March 3, 2012 No. 287-r, the only digital terrestrial television standard for Russia is the DVB-T2 standard. By Order of the Government of the Russian Federation dated May 24, 2010 No. 830-r, the performer of work within the framework of the federal target program “Development of television and radio broadcasting in the Russian Federation for 2009-2015” identified the “Russian Television and Radio Broadcasting Network”.

Ukraine

Test broadcasting of digital television in the DVB-T2 standard from the Kyiv television tower began on August 18, 2011.
On November 1, 2011, broadcasting in the DVB-T2 standard began in Ukraine.
Since February 2012, the DVB-T2 signal is encoded throughout Ukraine