Digital television signal quality dvb t2. Why does the signal quality fluctuate?
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 was chosen as the standard for digital 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 opportunities 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 one should not ignore the data transmission capabilities provided by the DVB-T2 standard. If previously a TV was only 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 broadcasting standard DVB-T2?
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 subscribers cable networks Over the course of several days, rare interruptions in the broadcast of individual programs could be observed.
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 about to buy a new TV, be sure to make sure that 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 enable digital tuner your TV (by selecting the country in the corresponding section of the settings menu - Poland, Lithuania or Germany). Then you should run automatic search channels - in most cases, a built-in signal level and quality indicator will allow you to optimally configure your antenna for receiving digital television.
If you need to manually configure 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 following 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".
master's student
Annotation:
The article provides an overview of the main features and advantages of the DVB-T2 digital terrestrial television standard. Quantitative indicators of the gain in performance of certain parameters of the new standard relative to old version DVB-T.
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.
Key words:
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 of 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 broadcast 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 together 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) - a code used in information transmission, special case block linear code with 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 about 30%, for example, due to the use of a higher level of constellation.
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 more easily detected and corrected 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 be performed over a longer period of 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 carriers, the so-called pilot carriers, or synchronization markers, are used for synchronization clock frequencies modulator and demodulator, synchronization of spectrum carrier frequencies, frame synchronization, estimation of channel state and phase noise level. 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 formed 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 different placement methods - 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 starts, 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 backward compatibility of the first transmission systems 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 fragments of each service will generally be transmitted to 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 the resistance to interference, picture quality, signal transmission speed and other indicators of the signal in the DVB-T2 standard are approximately 1.48 times better than DVB-T . Another undeniable advantage of 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: A new broadcast standard for high-definition television // Tele-Sputnik. 2008. No. 11.
3 Serov A.V. Terrestrial digital television DVB-T/N. SPb.: BHV-Petersburg. 2010.
4 Shakhnovich I. DVB-T2 is a new digital standard 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.
Seal
This is not a very common malfunction, and it cannot be called a malfunction, meaning when the quality of the received DVB T2 signal fluctuates. Most often this is due to the position of the cable from the antenna to the TV, reception conditions and a number of other reasons. Why this happens is simply incomprehensible to an inexperienced user in such matters, and he can explain this behavior of the tuner as a malfunction of the set-top box or antenna, but that is not the point. However, let's take things in order.
Reasons
The intensity with which the dvb-t2 signal jumps depends on the height at which the cable has such a horizontal section and how long it is; if it is located close to the ground, then the influence of interference is minimal. It is clear that the longer such a section is, the more the useful signal will be suppressed. To avoid this, place the antenna close to the set-top box; using a high-quality cable also helps.
The digital TV signal also begins to jump when it is tilted, for example when it descends from the ridge of the roof to the wall. It is worth noting that there is a known case when, with an inclined cable, the receiver showed for quite a long time after tuning, and with the onset of summer and hot weather, the signal level began to change abruptly from 0 to 100, and the quality signal remained at 5%.
There have been cases in practice when, in urban conditions, with a nearby tower located, an active indoor antenna was used to receive the first and second multiplex. The signal arriving at the tuner was very large, which led to the protection being triggered and, as a result, the signal began to jump on the digital tuner.
There were also opposite cases when the signal was artificially lowered. This refers to obstacles in the form of buildings or trees. Moreover, if there is a tree between the antenna and the tower, the reception is excellent in winter, but in summer the foliage dampens the signal and jumps in its level also occur. IN in this case It is enough to move the antenna. By the way, for this reason, the signal also fails on satellite TV; the installed dish was showing correctly for several years and suddenly glitches began to occur, the picture crumbles into squares. It turned out that the tree had grown over the years and began to block the dish from the satellite.
There are many nuances here and they can have an impact - weather, cable quality, range of the tower (signal strength), so you need to understand each case when the signal starts to jump when receiving or setting up T2, and it doesn’t matter what World Vision set-top box you have, Rolsen, etc..
Avoid twisting the wire into a coil, as well as long sections with horizontal and inclined cable positions; use in these cases.
To avoid interference, the cable must be placed away from power electrical wires and avoid crossing the cable with power lines, and when crossing, make it at a right angle.
Wire the TV cable in one piece; if breaks cannot be avoided, then use special connectors with reliable wire contact and shielding, and not twisted with electrical tape.
The DVB Consortium (located in Europe) developed DVB-T2 technology as an extension of the existing DVB-T standard to provide more efficient use of frequency resources through the integration of advanced signal processing technologies. With the new standard, up to a 50% increase in data transfer rates is expected when operating in the same frequency band.
Main features of DVB-T2
The specification is designed primarily for reception on fixed outdoor antennas and has the same frequency spectrum characteristics as DVB-T, which implies the possibility backward compatibility with the existing broadcast infrastructure...
Like DVB-T, DVB-T2 uses OFDM (orthogonal frequency division multiplexing) modulation and provides a range of modes with different numbers of carriers (1k, 2k, 4k, 8k, 16k, 32k, 16k extended, 32k extended) and modulation constellations (QPSK, 16QAM, 64QAM, 256QAM). For error protection, DVB-T2 uses LDPC (Low Density Parity Check) and BCH (Bose-Chowdhury-Hocquengham) coding. A new technique known as rotated constellations was introduced to provide additional stability in certain conditions.
The DVB-T2 standard also requires careful maintenance of transmission equipment. Particularly in 32k mode, high power peaks are generated and thus the amplifier's efficiency is minimized (or it may even fail). To limit these peaks without losing information, a special characteristic called PAPR (Peak to Average Power Ratio) reduction was introduced into the standard specification.
Comparison of DVB-T2 and DVB-T
| DVB-T2 | DVB-T | |
|---|---|---|
| FEC | LDPC + BCH | CC+RS |
| Encoding speed | 1/2, 3/5 , 2/3, 3/4, 4/5 , 5/6 | 1/2, 2/3, 3/4, 5/6, 7/8 |
| Constellation | QPSK, 16QAM, 64QAM, 256QAM | QPSK, 16QAM, 64QAM |
| Guard interval | 1/4, 19/256 , 1/8, 19/128 , 1/16, 1/32, 1/128 | 1/4, 1/8, 1/16, 1/32 |
| FFT size | 1K, 2K, 4K, 8K, 8K ext., 16K, 16K ext., 32K, 32K ext. | 2K, 8K |
| Distributed pilots | 1% , 2% , 4% , 8% of total carriers | 8% of total carriers |
| Continuous pilots | 0,35% of the total number of carriers | 2.6% of total carriers |
| Occupied frequency band | 1,7 ; 5; 6; 7; 8; 10 MHz | 5; 6; 7; 8 MHz |
| Maximum speed | 50.34 Mbps | 31.66 Mbps |
DVB-T2 system architecture
The main difference between DVB-T2 and DVB-T systems is that the multiplexer must be connected to a T2 gateway. This T2 gateway receives one or more multiplexes, that is, one per PLP, from the multiplexer and encapsulates them into unmodulated frames. The T2 gateway then sends this content to the DVB-T2 modulator using the T2-MI modulator interface protocol.
DVB-T2 frame structure
DVB-T2 borrows the PLP (or Physical Layer Link) concept introduced in the DVB-S2 specification. A PLP is a physical channel that can carry one or more services. Each PLP may have different data rates and error protection options. For example, you can separate SD and HD services into different PLPs. Another example is the DVB-NGH (New Generation Handheld) standard, which will be based on the ability to use multiple PLPs to enable mobile television broadcasting over DVB-T2.
The DVB-T2 standard defines several profiles:
If necessary, you can define a type (1 or 2) for each PLP, and then combine PLPs of different types in a T2 frame.
The T2 frame begins with preambles P1 and P2. The structure of a T2 frame is shown below.
DVB-T2 modulator interface
The T2 gateway encapsulates the data in an unmodulated (BaseBand) frame. These BB frames are sent to the DVB-T2 modulator using a special DVB-T2 modulator interface protocol MI, the structure of which is shown below.
DVB-T2 testing
Testing of the specification began in the UK in June 2008. The BBC, together with the broadcast network of operators Arqiva and National Grid Wireless, carried out the first test transmission in the DVB-T2 standard. In September 2008, at the IBC (Amsterdam), the DVB stand featured a series of presentations on the latest technologies, celebrating the latest achievements made by the DVB consortium in the field of digital terrestrial TV (DTT). For the first time, visitors to the stand saw HD content encoded using H.264 and delivered through the current end-to-end terrestrial TV broadcasting system using DVB-T2 technologies.
In the first DVB demonstrations, three HD channels were broadcast in one multiplex, each encoded at 11 Mbit/s latest version H.264 encoder. The signal was decoded by the BBC's latest H.264 demodulator and decoder and then displayed on an HD monitor.
At the second presentation, ENENSYS Technologies, NXP Semiconductors and Pace were recognized for the most reliable performance of DVB-T2 equipment. The purpose of this end-to-end demonstration was to show how the standard can handle injected noise and interference and, under such conditions, successfully process a DVB-T2 signal to provide excellent reception.
The first live multi-PLP broadcast was performed during Mediabroadcast's PlugFest in June 2010.
DVB-T2 technical testing in the UK
The BBC and Ofcom have been working on implementation various changes needed to modernize the first multiplex in the Granada region. This included DVB-T2 technical testing, which aimed to validate the DVB-T2 standard and determine the preferred transmission mode for approval in the UK. The tests, which included both laboratory tests and on-air transmissions, also served to provide a DVB-T2 signal to the receiving equipment being developed, which also needed to be tested.
For this purpose, a transmitter was recently installed for test broadcasting in the DVB-T2 standard from the Crystal Palace television tower. This was followed by the successful completion of end-to-end laboratory tests from the signal source to the receiver screen, made possible through the close collaboration between Arqiva and ENENSYS. ENENSYS provided a real-time DVB-T2 hardware modulator that was connected to Arqiva's transmission equipment.
This ambitious program will also support the DVB-T2 manufacturing community by providing test broadcasts for testing and developing new products. Prototypes of DVB-T2 receivers will soon become available and will be ready for use in a technical pilot project within the coming weeks or months.
Approval of the new DVB-T2 standard
UK telecoms regulator Ofcom has decided to upgrade one terrestrial digital television multiplex (Multiplex B) to operate the Freeview HD service using DVB-T2 and MPEG-4 standards. The upgraded multiplex will be capable of delivering HD services from BBC, ITV and Channel4. It is expected that delivery of six HD services will be possible over time. The first services were launched during digital transition(DSO) December 2, 2009.
In Finland, DNA Oy received a license to operate two DVB-T2 multiplexes. The trial began in December 2009 in the city of Lahti. The launch in Finland took place in November 2010.
In Italy, Europa7 launched seven HD channels in the spring of 2010.
In some countries, for example, Austria, Turkey, Serbia, Czech Republic, India, South Africa, Kenya, Sri Lanka, Singapore, Slovakia, Russia, Thailand, Vietnam, Malaysia, Australia have already approved or are seriously considering DVB-T2.
DVB-T2 Glossary
| Abbreviation | Transcript (English) | Transcript (Russian) |
|---|---|---|
| BB | BaseBand | Unmodulated, direct (transmit) |
| FEC | Forward Error Correction | Forward error correction |
| FEF | Future Extension Frame | Frame of future expansion |
| MISO | Multiple Input Single Output | Multiple inputs - one output |
| PAPR | Peak to Average Power Ratio | Peak power to average power ratio |
| PLP | Physical Layer Pipe | Physical Layer Channel |
| T2-MI | T2 Modulator Interface | T2 modulator interface |
| TI Block | Time Interleaving Block | Time interleaving block |
| TFS | Time Frequency Slicing | Time-frequency diversity |
| LDPC | Low Density Parity Check | Low Density Parity Check |
| BCH | Bose Chaudhuri Hocquengham | Bose-Chowdhury-Hocquengham coding |
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 operational, more than 70 countries around the world have deployed DVB-T broadcasting 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 the developers of an updated version of the standard, which was supposed to ensure even more efficient use of the frequency resource. The DVB-T2 system was able to satisfy all these requirements without any problems, 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 does this work?
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 code) 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:
- The use of several physical layer channels allows for separate adjustment of the stability of each of the transmitted programs within the channel to adjust to the required reception conditions (for example, an indoor antenna or external antenna). In addition, this function allows the receiver to save energy by decoding only a specific program from the multiplex, and not the entire transmitted package.
- 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 maximum speeds data transmission at a fixed signal/noise ratio and the required signal/noise ratio at a fixed (useful) 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. 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 Fast Fourier transform (FFT) values or different 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, as well as 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 broadcasting to digital standard DVB-T2, 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 in which the introduction of digital broadcasting in the DVB-T2 standard began 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 national network on-air digital broadcasting "Zeonbud" 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 according to 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 obligations to switch to digital by July 17, 2015 on time.
Note that paid DVB-T2 platforms were also 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 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.