Master came in, three questions about digital TV.

The advantages of digital TV transmission system mainly come from channel coding and signal modulation. Satellite and CATV network environment is very close to the ideal white noise model, and excellent channel coding and signal modulation methods are generally designed for the white noise model. Such channel coding and modulation can be well applied to satellite and cable broadcasting, and the system performance can be close to the theoretical value. However, the environment of terrestrial broadcasting is obviously not a white noise model, and no channel coding modulation technology can be used optimally in terrestrial broadcasting environment. The existing systems in the United States and Europe reflect this feature: in the white noise environment in the laboratory, both systems are close to the theoretical value, but once in the actual terrestrial broadcasting environment, the performance of both systems is obviously deteriorated. Although American system is superior to European system in white noise performance, American system does not consider serious multipath environment and fading phenomenon, and its ability to receive actual terrestrial broadcast signals is weaker than European system. In fact, the gain coding of the existing system under the condition of white noise not only does not help to improve the performance in the actual environment, but aggravates the deterioration of the system performance. The channel characteristics of terrestrial broadcasting change dramatically, and the changes of signal amplitude and phase, multipath delay and amplitude are far more complicated than those of satellite and wired channels. The stable working area of the system is limited, which requires high signal processing ability, especially processing speed and stability. In addition, terrestrial broadcasting requires compatibility with existing analog TV broadcasting, and high-power nonlinear transmission intensifies the interference between adjacent channels. If all the links of the system's error-correcting coding protection can't be well coordinated, one will lose sight of the other, and the performance of each part will restrict each other, making the system always in an unstable state. Therefore, how to adopt a digital TV terrestrial broadcasting transmission system standard with strong adaptive function under the harsh conditions of multi-channel terrestrial broadcasting is a problem that every radio and television technician thinks about. Based on three transmission performances and implementation methods of digital TV terrestrial broadcasting system abroad, this paper discusses the anti-multipath interference technology, spectrum, standard formulation, efficient utilization of spectrum, data transmission, stable fixed reception and mobile reception ability, which provides reference for the main design of the system.

Second, the standard of terrestrial digital TV transmission system

At present, there are three sets of terrestrial transmission system standards in the world. The trellis coded 8-level vestigial sideband (8-VSB) developed by American Advanced Television Systems Committee (ATSC) in 1996 is ATSC 8-VSB; Digital video terrestrial broadcasting (DVB-T) proposed by Europe 1997 adopts coded orthogonal frequency division multiplexing (COFDM), namely: dv b-T COFDM；; ; The ISDB-T proposed by Japan in 1999 adopts orthogonal frequency division multiplexing (OFDM), that is, ISDB-T OFDM. The system design of these three system standards is technically limited to the design direction, use environment, technical level and hardware support ability at that time, and has not played its due potential.

1, American ATSC 8-VSB system

The American ATSC 8VSB system is designed to transmit high-quality video and audio (HDTV) and auxiliary data in a single 6MHz channel for terrestrial broadcast distribution system. It can reliably transmit 8VSB modulated 19.4 Mbit/s data within 6MHz. 8-VSB "terrestrial simulcast mode" can resist NTSC interference. For terrestrial broadcasting, the design of the system allows additional digital transmitters with comparable coverage to be assigned to existing NTSC transmitters, and has minimal impact on existing NTSC programs in terms of regional and population coverage. After carefully selecting the RF emission characteristics of the system, the above capabilities can be realized, and various image qualities can be provided through the 18 video format. Using the data transmission capacity of the system, data-based services have great potential. The system provides fixed reception.

Add 0.3dB pilot signal to 8-VSB system to assist carrier recovery. The segment synchronization signal is added to protect the synchronization of 8-VSB system and the error correction of clock channel coding. This design makes the American system have low noise threshold (theoretical value ≈ 14.9dB), large transmission capacity (fixed useful data bit rate is 19.4Mb/S), serial data stream MPEG-2 packet 188 bit (1 bit synchronization+1). But there are a series of problems in the American system. The most important thing is to deal with the difficulty of strong dynamic multipath: when the near-strong multipath changes (phase), the pilot signal will be seriously affected and carrier recovery will be difficult. At the same time, when the carrier is not accurately recovered, the performance of the equalizer will drop sharply; Although the training sequence is used in the system, the interval between two training sequences is 24 milliseconds, so it is impossible to track the rapid change of multipath. Although the American system uses the data decision feedback "DFE" to track the fast-changing multipath by adjusting the error signal generated by the data itself, the DFE needs a certain degree of channel balance (the error decision is less than 10%) to work normally, and the system is unstable under strong multipath. So the initial design ideas, pilot placement, data structure, etc. This makes the system unable to effectively deal with strong multipath and fast-changing dynamic multipath, which leads to unstable fixed reception and does not support mobile reception in some environments. In addition, the American system uses comb filter when dealing with analog TV simulcast. When the comb filter is turned on, the system threshold rises by 3dB, and whether it is turned on or not is a hard switch after judgment. In practical application, this scheme will not only make the switch jump back under the influence of noise or multipath change, resulting in unstable system operation, but also affect the system grid decoding and equalizer work because of the series and 12 interleaving. ATSC 8-VSB transmission system has a good carrier-to-noise ratio and can work at a low carrier-to-noise ratio. However, a comb filter is added to the receiver to resist NTSC synchronous interference, but the carrier-to-noise ratio performance is about 3.5dB. In order to resist frequency selective fading caused by multipath effect, 8VSB transmission mode uses equalizer to eliminate echo, but it is sensitive to echo delay change; The structure is complex, it is a digital transmission system with fixed bit rate, which adopts single carrier modulation technology and does not support mobile reception.

2. European DVB-T COFDM system

European DVB-T COFDM system is a digital terrestrial television broadcasting system standard in a series of standards formulated by European Digital Television Broadcasting (DVB), and DVB-T is the most complicated DVB system in this series of standards. Using MPEG-2 transmission bit stream multiplexing and Reed-Solomon (RS) forward error correction system, the transmission bits are divided into thousands of low bit rate subcarriers by COFDM modulation, using 1705 carrier ("2K") or 68 17 carrier ("8K"). "2K" mode is used for ordinary networks, "8K" mode is used for large and small single frequency networks (SFN), and "2K" and "8K" systems are compatible. In the European system, a large number of pilot signals are inserted into the data and transmitted at a power of 3dB higher than that of the data. These pilot signals have many uses, such as system synchronization, carrier recovery, clock adjustment and channel estimation. Because the number of pilot signals is large and scattered in the data, the change of channel characteristics can be found and estimated in time. In order to further reduce the inter-symbol interference caused by multipath, the European system also adopts the technology of "guard interval", that is, a certain length of repeated value is added before each symbol (block) to resist the influence of multipath. It can be considered that the technology of inserting a large number of pilot signals and guard intervals is the technical core of the European system, and it is these two technologies that make the European system superior to the American ATSC 8-VSB system in the measured performance of resisting strong multipath and dynamic multipath and mobile reception. In addition, the European system also combines the number of carriers, the length of guard interval, the number of modulation constellations and other parameters to form a variety of transmission modes for users to choose from. In fact, there are only two or three commonly used modes, corresponding to fixed reception and mobile reception applications respectively. The European system also has a series of defects. First, the frequency band loss is serious: the pilot signal and the guard interval account for at least about 14% of the effective bandwidth, and if a large guard interval is adopted, this value will exceed 30%. The comprehensive band utilization rate of European scheme is 6% to 23% higher than that of American VSB scheme. Therefore, it is obviously not a good compromise to exchange the anti-multipath performance of the system at the expense of excessively reducing the precious transmission capacity of the system. Secondly, even if a large number of pilot signals are placed, the channel estimation is still insufficient: the pilot signal in COFDM is an undersampled signal, and COFDM adopts a block signal processing method (one thousand points at a time), which can not completely and accurately describe the channel characteristics in theory and can only give an approximate average value, which is one of the reasons why the European system can never reach the theoretical value (2-3dB difference from the theoretical value). Therefore, the existing European COFDM system is actually not the third, and the performance of European system in interleaving depth, anti-impulse noise interference and channel coding is obviously insufficient. Europe also emphasizes the use of the same channel coding module in its satellite, cable and terrestrial transmission schemes to ensure their compatibility, because the proportion of channel coding modules in circuit implementation is very small, and this partial compatibility prevents the adoption of more effective other channel coding methods in terrestrial broadcasting schemes. For terrestrial broadcasting, the system can select the transmission rate of 3.7-23.8Mb/S in the existing UHF spectrum allocated for analog TV transmission. Although the system is developed for 8MHz channel, it can be used for any channel bandwidth (6, 7, 8MHz), but the data capacity changes accordingly. The effective net bit rate of 8MHz channel transmission is in the range of 4.98~3 1.67Mbit/s, which depends on the selection of channel coding parameters, modulation type and guard interval. The code rate is allowed to be variable in the design, which reflects its flexibility and can provide multiple code rates according to the signal-to-noise ratio. DVB-T COFDM system is beneficial to the storage of digital TV and analog TV, and shows advantages in mixed transmission with existing analog TV. It can deal with the interference of various analog systems without optimization in design. It has the ability to resist multipath distortion, which shows its unique advantages in mobile reception. It is praised in Australia, Latin America and Hong Kong because it can flexibly carry out transmission experiments according to specific working environment and service requirements.

3. ISDB-T OFDM system in Japan

The ISDB-T OFDM system of "Integrated Service Digital Broadcasting" proposed by Japan adopts MPEG-2 transmission bit multiplexing and OFDM modulation, and the coding mode, modulation and transmission used are basically the same as DVB-T COFDM, which can be said to be an improved European mode. The difference is that partial reception and layered transmission are added to the reception, and the whole 6MHz frequency band is divided into 13 subbands. Each subband is 432KHz, and the middle one is used to transmit audio signals, which greatly extends the interleaving depth (up to 0.5 seconds). Increasing the interleaving depth will introduce a delay of several hundred milliseconds, which will affect channel switching and two-way service. ISDB-T covers all kinds of services, so the system has to face all kinds of requirements, and one service may be different from another. For example, for HDTV programs, large transmission capacity is needed, while for key transmission and software download in conditional access, high efficiency (or transmission reliability) is needed. In order to integrate different business requirements, the system provides optional modulation and error protection schemes and flexible combinations to meet each demand of these integrated services.

A terrestrial channel has 13 OFDM bands, and the available bandwidth is13× bw/14 MHz (5.57MHz for 6 MHz channel, 6.50MHz for 7MHz channel and 7.43MHz for 8MHz terrestrial channel). The modulation method used in the system is called Band Segmented Transmission (BST)OFDM, which consists of a group of basic frequency blocks called BST segments. Bandwidth of each segment is BW/ 14 MHz, where BW refers to the channel bandwidth of terrestrial TV (6, 7 or 8MHz, depending on the region). For example, in a 6MHz channel, each segment occupies 6/ 14 MHz = 428.6KHz spectrum, and 7 segments are equal to 6×7/ 14MHz = 3MHz.

In addition to OFDM characteristics, BST-OFDM uses different carrier modulation schemes and inner code coding rates for different BST segments, providing layered transmission characteristics. Each data segment has its own error protection scheme (inner code coding rate, time interleaving depth) and modulation type (QPSDQPSK, 16-QAM or 64QAM), so each data segment can meet different business requirements. Many segments can be flexibly combined to provide broadband services (such as HDTV). By transmitting OFDM segments with different parameters, layered transmission can be realized. Three service layers (three different segment groups) can be provided in the terrestrial channel. By using a narrowband receiver with only one OFDM segment, some programs in the transmission channel can be received.

Although the system is developed and tested for 6MHz channel, it can be used for any channel bandwidth (X×BW/ 14 MHz), but the data capacity will change accordingly. The net bit rate of each segment in the 6MHz channel is 280.85 ~ 1787.28 kbit/s, and the data throughput of the 5.57MHz DTV channel is in the range of 3.65 ~ 23.23 mbit/s.

4. Comparison of three terrestrial digital TV transmission systems.

Performance of ATSC 8-VSB, DVB-T COFDM and ISDB-T BST-OFDM transmission systems under different damage and operating conditions.

From the modulation point of view, OFDM and single carrier modulation schemes, such as VSB and QAM, should have the same C/N threshold for AWGN channels. Channel coding, channel estimation, equalization scheme and other implementation constraints (phase noise, quantization noise, intermodulation distortion) lead to different C/N thresholds.

The data rate and threshold determine the difference, and the Eb/N0 threshold of AWGN channel is shown in Table 2. DVB-T and ISDB-T choose two convolutional coding rates, R=2/3 and 3/4, which improve the data rate equivalent to ATSC system. According to the RF back-to-back test data, ATSC system currently has several dB benefits on AWGN channel. Once again, it should be pointed out that all systems can be improved. For DTTB, AWGN channel may not be the best channel mode, especially for indoor reception.

Because three systems can be used for different channel bandwidths without changing the channel coding scheme, such as 6, 7 and 8MHz, the Eb/N0 value of the system is usually correct for 6, 7 and 8MHz systems. For terrestrial broadcasting,

Thirdly, anti-multipath interference technology.

Multipath reception is a ghost in analog TV, but in digital reception, multipath effect will make reception completely ineffective. In terrestrial digital TV transmission, frequency selective fading caused by multipath effect will cause intersymbol interference and produce error code. Therefore, anti-multipath interference technology must be adopted in terrestrial digital TV transmission. There are adaptive equalization and orthogonal frequency division multiplexing technologies at present. The algorithm adopted by the adaptive equalizer is least mean square (LMS), which is based on least square (LS) and fast transversal filtering algorithm:

K=-N，- 1，0， 1，…M

Finding the minimum mean square error enables the equalizer to eliminate ISI most effectively.

OFDM Orthogonal Frequency Division Multiplexing (OFDM) modulation technology is a parallel transmission scheme. It is an effective method to resist multipath interference by setting K equal-spaced subcarriers in the specified frequency band and digitally modulating each subcarrier, and the modulation symbols on each subcarrier will be expanded by K times. It is realized by increasing the guard interval and reference level.

In a symbol time interval, it is assumed that the baseband OFDM signal is expressed as:

Where M(n) represents the modulation signal of the nth subchannel, and n is the number of parallel transmission channels.

In order to improve the anti-multipath interference ability, the guard interval is increased, so the symbol width becomes T=T5+△, and the channel interval is still the same. At time t, the OFDM signal is:

After multipath channel, the orthogonality between subchannels is destroyed. Assuming the number of transmission paths with relative delay less than M 1 and greater than M2, the demodulation output of the kth channel at the ith time is:

In the above formula, the first term is useful signal, the second term is inter-channel interference, the third term is inter-symbol interference, and the fourth term is white noise. If the guard interval is long enough so that the relative multipath time difference is less than △, there will be no inter-symbol interference and inter-channel interference in the demodulated signal. (When T=64- 192us and △ = 20, multipath interference in terrestrial broadcasting can be basically eliminated. )

However, the useful output signal will also be affected by multiplicative interference, so it is necessary to insert reference level signals alternately in each subchannel to obtain the inverse response of the channel and correct the amplitude and phase of the received signal to eliminate multipath effect. In addition, the combination of time interleaving, frequency interleaving, guard time and coding is helpful for OFDM to improve its anti-multipath interference ability and effectively use the energy of multipath interference signals.

The OFDM modulation systems adopted by DVB-T and ISDB-T have strong anti-multipath distortion ability and can resist echoes as high as 0dB. In urban areas, when indoor or set-top antennas are used, because the linear path of the transmitter is blocked, large echoes are usually generated. The guard interval can completely eliminate intersymbol interference unless the echo delay exceeds the range of the guard interval. In any case, in-band fading will still affect the required C/N, especially when high-order modulation is used on COFDM carrier. In order to resist the strong echo of 0dB, DVB-T and ISDB-T need strong inner code error correction, good channel estimation system and high C/N. When using R = 2/3 convolutional code, it needs about 6dB more signal power to process 0dB echo. In any case, a part of the increased C/N can be compensated by the echo signal power. The balance of these requirements will depend on the selected code rate. Soft decision decoding using cancellation technology can significantly improve performance.

The guard interval of DVB-T and ISDB-T systems can be used to deal with multipath distortion in advance or delay. This is very important for the operation of SFN (Single Frequency Network). ATSC system can't deal with long front echo, because it is designed for MFN (Multi-frequency Network) environment, and they usually don't produce long front echo in the case of outdoor fixed reception. Because all transmitters in an area work at the same frequency and bring some network gains by increasing the probability of receiving signals from multiple transmitters, SFN can significantly save spectrum requirements and transmission power.

Fourth, spectrum efficiency.

As a multi-carrier modulation scheme, the spectral efficiency of OFDM is slightly higher than that of single-carrier modulation system, because its initial spectrum roll-off is very fast, even without an output spectrum shaping filter. For 6MHz channel, the useful bandwidth (3dB) of DVB-T system is 5.7MHz (or 5.7/6=95%), and that of ISDB-T system is 5.6MHz (or 13/ 14 = 93%). In contrast, the useful bandwidth of ATSC system is 5.38MHz (or therefore, OFDM modulation has a spectral efficiency advantage of at most 5%.

In any case, the guard interval used to cancel multipath distortion in DVB-T and ISDB-T systems and the in-band pilot inserted for fast channel estimation will reduce the data capacity. For example, DVB-T provides the choice of system protection interval, which is 1/4, 1/8,1/6, 1/32 of the actual symbol duration, which is equivalent to the reduction of data capacity by 20% and132 respectively. In-band pilot insertion of112 will result in 8% bit rate loss. Overall, for different protection intervals, the data throughput will be reduced by 28%, 19%, 14% and 1 1%. Subtract the 5% bandwidth efficiency advantage of OFDM system, and the total data capacity of DVB-T system is reduced to 23%, 14%, 9% and 6% respectively compared with ATSC system. This means that for the 6MHz system, assuming the same channel coding and modulation scheme (64QAM, r = 2/3), the DVB-T system will provide 14.9, 16.6, 17.6 and18./kloc as mentioned above. ISDB-T system will provide data rates of 14.6, 16.4, 17.2 and 17.7Mbit/s; The corresponding ATSC system code rate is fixed at19.4 mbit/s.

In fact, DVB-T and ISDB-T systems can adapt to various transmitters, thus expanding coverage and improving spectrum efficiency. Based on MFN (multi-frequency network) environment, DVB-T has the following advantages: it is suitable for harsh multipath environment; Fast moving multipath environment; Single frequency network SFN；; ; Mobile reception; And that position of the non-directional receive antenna. However, in SFN environment, many transmitters can use the same frequency (channel) to cover a huge range, which will lead to the overall saving of spectrum and transmission power of DVB-T and ISDB-T systems.

Five, the development of digital TV terrestrial transmission standards.

The transmission scheme will constitute the basic technical content of a national digital TV terrestrial broadcasting transmission standard. As a big country in TV production and consumption, as a developing country that is integrating into global economic integration and facing global technical competition, China has realized that mastering and possessing key technologies and independently developing important digital TV system standards can bring huge development space and opportunities to China's economy. In order to expand the world market and obtain high technical profits, the world's advanced industrial countries have spared no effort to recommend their standards to China in recent years by virtue of their leading technological advantages and industrial base. In particular, the proposal focuses on the transmission standard of digital TV terrestrial broadcasting, aiming at promoting the system standard to fully adopt its entire standard series. In this regard, we should have a comprehensive and objective understanding of the necessity and feasibility of independent research and development of transmission schemes.

The ground system consists of a TV transmitting station and a TV station. The coverage of a single station is small and needs to be updated one by one. Moreover, the corresponding domestic standards are still under study, and it will take some time to determine. However, the transition period after the establishment of terrestrial digital standards in the United States, Japan and other countries is about 10 years, and China is even slower. Terrestrial digital TV usually starts from big cities and developed areas. For example, China is likely to start from Beijing, Shanghai and Shenzhen. The Tenth Five-Year Plan of China Radio, Film and Television shows that in 2003, the transmission standard of digital TV terrestrial broadcasting will be formulated and the digital TV test bed will be established. By 2005, radio stations and television stations at or above the provincial level will basically realize digitalization of editing and broadcasting, and the national radio and television system will basically realize networking. By 20 10, the production, broadcasting, transmission, transmission and reception of radio and television programs will be basically digitized, and by 20 15, the transition from analog to digital will be completed.

The driving force of promoting digital terrestrial television in China is quite different from that in foreign countries. American families are mostly scattered wooden houses, and terrestrial TV mainly focuses on local programs. In China, terrestrial transmission is no longer the only way when black-and-white and color TV were just developed. At present, satellite and wired transmission methods are very mature. Cable TV is the main transmission mode in cities, and satellite is the main transmission mode in remote areas and rural areas. Most urban residents no longer use outdoor antennas to receive TV programs, but use cable TV. It is difficult for high-rise residents to use indoor antennas, and many buildings are either shielded or oriented in the wrong direction. In a family with cable TV, it is very inconvenient to require users to receive a set of HDTV with indoor antenna while receiving cable standard definition TV. Considering that the equipment required for cable transmission of HDTV is exactly the same as that for ordinary HDTV. Therefore, in the development of HDTV, the importance of terrestrial transmission is completely different from that of black-and-white and color TV in the early stage of development.

How to popularize terrestrial digital TV in China, what standards to choose, what programs to broadcast and what policy guidance to provide are all problems to be solved. China has the national conditions of China, which is different from the United States and Europe. What are the advantages of using terrestrial digital TV broadcasting? Why does the United States promote digital terrestrial broadcasting? The first reason is to save frequency resources. At the end of analog-to-digital conversion, the FCC in the United States can completely restore the VHF band and gradually charge TV frequencies. The second reason is that it can start the demand of American digital TV market. There are similar reasons for promoting DVB-T in Britain. Therefore, the analysis of digital TV in China should be carried out under two different conditions. First, there is no charge for the frequency of TV stations, and there is no rigid time-limited conversion. Because China is a developing country, television is the most important tool for ordinary people to entertain and get information. The second is to promote China's industries, most importantly, TV industry, chip industry and software industry. At this time, the power of terrestrial digital TV broadcasting comes from market and policy. Terrestrial digital TV should be able to receive not only fixed, but also portable and mobile. Procedure is another important factor. If digital programs are the same as analog programs, the viewing quality will be improved to some extent compared with the original analog cable TV, but the improvement is not great. Users don't have to spend hundreds of dollars to buy a set-top box to watch almost the same quality programs. Some people think that maybe a better scheme can be used to promote digital TV, but if you already have a better scheme, the analog scheme without buying a set-top box may have better economic benefits and faster returns. The production of digital programs and the investment in set-top boxes may completely offset the economic benefits brought by good programs, or few people will invest in such an invisible market. It has also been pointed out that the market of the number 16: 9 has received a good response in Europe, because the benefits brought to the audience by ordinary definition 16: 9 are really insignificant compared with the improvement of the studio and the increase of the price of the receiver. China now has a high definition 16: 9 TV, which will soon enter the market. Therefore, the key to the development of terrestrial digital TV in China lies in HDTV. Terrestrial digital broadcasting can play a whole set of high-definition TV programs on the original ordinary analog TV channels, and the clarity and sound quality have been greatly improved, so it can become a real home theater. The original worry about the price of HDTV has also dropped a lot. First of all, it has a good market prospect.

Under the organization of the government, China has carried out the research and development of digital HDTV system technology for nearly ten years, and has successfully developed two generations of digital HDTV terrestrial broadcasting prototype systems, and conducted on-site signal relay experiments. Through the joint efforts of scientific research, broadcasting and technical personnel from all walks of life in the industry, a variety of realization schemes with independent patented technologies have gradually formed, especially in the field of digital TV terrestrial transmission technology. For example, the "Digital Multimedia Television Broadcasting Transmission System DMB-T" independently developed by Tsinghua University adopts OFDM multi-frequency modulation technology, and the maximum payload rate is 33Mb/s within 8MHz bandwidth. In the whole system design, foreign ready-made chips are not used, and every step is designed independently, realizing completely independent intellectual property rights, which has great market potential. At present, the technology has completed the stage of computer simulation and FPGA prototype verification, and entered the stage of patent application and practical application. At the same time, the country plans to test and compare the performance of existing transmission schemes at home and abroad. Based on the existing research foundation and advancing speed, it is entirely possible for China, with the full support of government departments at all levels, to formulate China digital TV terrestrial broadcasting transmission standard with its own characteristics and independent intellectual property rights in a relatively short period of time through testing, analysis and improvement.

China's current TV broadcast channel bandwidth is 8 MHz, which is basically the same as that of Europe, but different from that of the United States and Japan. The spectrum allocation and planning of terrestrial broadcasting channels in China is complicated, which is determined by the current political, cultural and economic situation in China. Its digital TV programs and other business forms do not fully meet the needs of developed countries. The transmission standard scheme formulated in China should strive to meet the following technical requirements: try to meet the requirements of digital TV terrestrial broadcasting, the system has two main working modes: fixed reception and mobile reception, and adopts anti-multipath interference technology to make the system receive stably in strong multipath and dynamic environment, and at the same time improve the spectrum efficiency and ensure the transmission data capacity of the system. Considering that digital terrestrial broadcasting and cable broadcasting may constitute the main market of digital TV broadcasting in China in the future, the developed terrestrial transmission scheme should make its receiver easy to be compatible with digital cable demodulation and decoding scheme. In other words, the system should be compatible with the digital cable scheme. The system should strive to overcome the shortcomings of the above-mentioned foreign systems and form its own system composition and data structure. The system should form the design scheme of receiving chip as soon as possible, and China enterprises should first apply for the patent of receiving technology and successfully develop the standard scheme.

Ending of intransitive verbs

Through the above discussion and analysis, it can be concluded that the digital TV terrestrial broadcasting system can realize efficient spectrum utilization, large enough data transmission capacity and stable fixed reception and mobile reception capabilities. In order to save transmission bandwidth, digital TV broadcasting system should adopt modulation technology and channel coding to improve transmission reliability, so that each Hz band can transmit more bits (data rate). The standard we adopt should be a digital TV terrestrial broadcasting system that can stably realize large data capacity transmission in both fixed and mobile receiving environments. On the basis of existing foreign standard schemes, China is currently studying and formulating its own digital TV standard, which has accumulated considerable practical experience in the field of terrestrial broadcasting transmission and has a good research foundation. As long as we continue to make unremitting efforts and absorb the essence of modern technology with the support of the government, it is entirely possible to form a transmission standard scheme with advanced technology and superior performance. This will have a far-reaching impact on the healthy development of China digital TV industry and even the whole electronic consumer market.