The future of analog TV curtain call is not just clearer images
2020 is coming to an end, and we are leaving with it, and there are analog TVs that have accompanied the growth of generations of Chinese.
At 11:59 pm on November 30th, Hong Kong terminated analog TV broadcasting and officially entered the era of full digital TV broadcasting on December 1.
According to the “Notice Concerning the Relevant Work Arrangements for the Shutdown of Terrestrial Analog Televisions According to the Plan” issued by the State Administration of Radio and Television in July this year, the terrestrial analog television signals of CCTV programs across the country will be released before August 31. The signal will complete the shutdown before December 31, and the shutdown will be completed before March 31, 2021 at the latest under special circumstances.
The transition from analog to digital is a key upgrade of TV technology. As we enter full-scale digital TV, analog TV will also withdraw from the stage of history forever.
What are the advantages of digital TV compared with analog TV?
What value will the spare spectrum signal play after the analog TV is fully retired?
Digital coding brings higher transmission efficiency
It is understood that the analog signal refers to the information expressed by continuously changing physical quantities, and the amplitude, frequency or phase of the signal will continuously change over time.
For example, temperature, humidity, current, voltage, etc., these physical quantities can have an infinite number of different values within a certain time range, and they can all be represented by analog signals.
In the process of analog signal transmission, the information signal needs to be converted into almost "identical" fluctuating electrical signals (hence called analog signals), and then transmitted through wired or wireless means. After the electrical signals are received, they can be passed through the receiving device. Revert to an information signal.
The widespread application of analog signals began in the early 20th century. In the telephone system at that time, sound signals were converted into electrical signals, which were then transmitted along wires and detected and analyzed by the receiving device at the other end.
In this process, the longer the transmission distance, the weaker the electrical signal, coupled with the noise interference in the line, will greatly reduce the quality of the call.
In order to solve this problem, the founder of information theory, Claude Elwood Shannon, proposed a plan: convert language into simple code, detect audio signal and then sample, and convert the fluctuation frequency value of each sampling point to 0 The code composed of and 1 forms a long string of codes and then transmits it along the line.
Through this encoding method, the receiving end can reconstruct the original audio signal.
This is the prototype of the digital signal.
Later, in addition to sound, text and images can also be encoded as 0 and 1 for transmission.
So what is the difference between an analog TV signal and a digital TV signal?
"Analog TV signals are mainly composed of image signals and audio signals, which are modulated on a radio frequency carrier by means of amplitude modulation and frequency modulation. After the receiver separates the received signals, the image signals and audio signals are respectively amplified, and finally decoded and converted by a picture tube and a speaker to show The TV programs we have seen." Song Li, deputy director of the Institute of Image Communication and Network Engineering of Shanghai Jiaotong University, told a reporter from Science and Technology Daily.
The digital TV signal starts from the source, and encodes each pixel of the image and each syllable of the accompanying sound with binary numbers. After source compression coding and channel coding, it is transmitted and transmitted in the form of bit rate. , The image and sound can be restored after decoding at the receiving end.
"In essence, with limited bandwidth, digital signals can transmit more information than analog signals. The transmission efficiency and spectrum utilization are higher. The more information is transmitted, the sound and picture quality of the TV will naturally be better." Song Li For example, a terrestrial analog TV channel with 8MHz bandwidth can only transmit one set of programs, while terrestrial digital TV uses digital compression technology, which can transmit multiple sets of broadcast television programs under the same 8MHz bandwidth.
The "snowflakes" on the analog TV screen are memories of many people. In fact, the scientific name of these "snowflakes" is "noise".
When the TV antenna is receiving a signal, it will accidentally pick up external electronic noise and radiated electromagnetic noise, which will appear as flowing random pixels on the screen, accompanied by harsh noise.
Terrestrial digital TV will not have the "snowflake" phenomenon that is common in analog TV, because its encoding transmission method is more reliable, anti-interference ability, and receiving sensitivity are higher, so it can provide higher definition TV programs.
Full digitalization also faces double constraints
Switching from analog TV to digital TV is not only a change of old and new technology, but also a necessity under the wave of digitalization.
As early as 1999, at the military parade on the 50th anniversary of the founding of the People's Republic of my country, full HD digital TV was used for live broadcast.
"Digital TV related technologies appeared earlier, but the elimination of analog TV and the large-scale and commercial application of digital TV are a slow process." Song Li said.
Due to the large differences in the geographical environment of various countries, coupled with the presence of signal shadowing effects in transmission and mobile reception and other tests, terrestrial digital television must consider the actual situation when formulating and selecting standards.
Therefore, the dual constraints of the natural environment and technology have delayed the advancement of terrestrial digital television signal transmission in most countries to a certain extent.
It is understood that the transmission methods of digital TV signals are mainly divided into three types: cable transmission, terrestrial transmission and satellite transmission.
Song Li explained: “For digital TV signals, the cable transmission method has a relatively low attenuation rate. However, after terrestrial signal transmission or satellite signal transmission arrives indoors, there will be a certain penetration loss, resulting in severe signal attenuation. In a mobile scene, the Doppler effect can also cause signal attenuation."
Song Li believes that as 4K/8K high-definition TV becomes the mainstream trend, higher bandwidth is required to transmit digital TV signals. Therefore, spectrum resources must be expanded to solve the problem of insufficient transmission efficiency under limited bandwidth.
"For example, the development of more advanced transmission technologies such as NOMA technology (non-orthogonal multiple access technology), terahertz transmission technology, air-space-ground integration, and the development of more advanced electronic components to form new solutions." Song Lee said.
There is still much to be done to optimize the digital TV experience.
"For example, let more urban buildings use public antennas, so as to effectively solve the problem of penetration loss of fixed TV reception; integrate the ground radio and television signal transmission and mobile communication networks, so as to achieve packet loss in terrestrial radio and television transmission (in the process of data packet transmission) In case of loss), the mobile communication network is used to supplement the package. With its natural common efficiency, the radio and television network can share the traffic for the mobile communication network and enhance the intrinsic value of the digital TV network." Song Li said, "No sense of supplementary package can be more It can improve the experience of digital TV in the mobile scene, and personalized interaction through the mobile network can stimulate the vitality of terrestrial digital TV."
The deep integration of radio, television and communications has become a trend
In the first half of this year, the Ministry of Industry and Information Technology issued the "Notice on Adjusting the Frequency Use Plan of the 700MHz Frequency Band", stating that "the 700MHz frequency band plan will be used in mobile communication systems to provide valuable low-frequency spectrum resources for the development of 5G, which can promote 5G Coordinated development of high, medium and low frequency bands".
It is understood that this part of the spectrum resources vacated belongs to the low frequency band and is of high quality.
"The transmission and receiving devices of this frequency spectrum are easier to make and the cost is low, which can bring more abundant transmission resources to the mobile communication system. On the other hand, when using ultra-high bandwidth (such as terahertz, millimeter wave), related devices, The production of materials is difficult and costly." Song Li said.
At the 700MHz technology and industrial application seminar held on December 7, Zeng Qingjun, deputy general manager of China Radio and Television Network Co., Ltd., said that how China Radio and Television and the traditional three major operators can avoid homogeneous competition and form differentiated development. A major issue, the breakthrough point China Radio and Television has found is 5G NR broadcasting.
It is understood that 5G NR is a global 5G standard based on a new air interface design based on a digital multi-carrier modulation method, and is also a very important cellular mobile technology foundation for the next generation.
5G NR broadcast does not change the existing system of 5G transmission layer and physical layer. It uses 5G existing NR channels for 5G network deployment. It is a combination of 5G technology and broadcasting services and can realize the integration of 5G broadcasting and 5G communication networks.
Compared with traditional broadcasting technology, it has more comprehensive functions and a wider range of application scenarios.
It is reported that in October this year, China Radio and Television has successfully conducted 5G NR broadcast experiments in conjunction with Huawei and other manufacturers.
"Using radio and television transmission towers and mobile base stations, that is, using 5G modulation and channel mode, and 5G group wave and single wave modules to broadcast digital TV. For the entire radio and television industry, it is an important development technology choice." Zeng Qingjun said, After the technology is mature, any operator's 5G terminal can receive radio and TV programs for free in the future.
Intern reporter Dai Xiaopei