In order to improve the transmission quality of satellite radio and television signals and facilitate more users to listen to radio and watch TV, on August 1, 2007, China adjusted the satellites for satellite radio and television signal transmission, and originally passed Asia 3S and Asia 4 The central and provincial satellite radio and television programs transmitted by Asia-Pacific No. 6, Asia-Pacific 2R, Zhongwei No. 1 and Xinnuo No. 1 were adjusted to Zhongxing 6B and Xinnuo No. 3. On June 9, 2008, China successfully launched the first direct broadcast satellite dedicated to radio and television coverage. The successful launch of Zhongxing 9 further promoted the development of satellite live TV in China. This article will make a distinction from the technical point of view of the three major satellites that currently undertake satellite radio and television signal transmission tasks in China.
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Comparison of the basic situation of three satellites
The satellite No. 9 is a high-power, high-reliability, long-lived broadcast television broadcast satellite, fixed at 92.2 degrees east longitude over the equator, using the ITU-defined BSS band, with four 54MHZ and 18 36MHZ transponders. . The main coverage area is China (including Hong Kong, Macao and Taiwan).
Zhongxing 6B is fixed at 115.5 degrees east longitude and has 38 C-band transponders with a bandwidth of 36 MHz. It mainly covers China, Mongolia, Korean Peninsula, Japan, Russia, Asia, South Asia, Southeast Asia, Central Asia, West Asia, Australia and New Zealand.
Xinnuo No. 3 is fixed above the equator at 125 degrees east longitude. It is a C-band broadcasting dedicated communication satellite. It has 10 C-band transponders with a bandwidth of 36 MHz, covering all parts of China and surrounding countries and regions. The EIRP of satellites in China exceeds 40DBW, and the quality factor G/T of each provincial capital city is greater than 0DB/K, which fully meets the requirements for transmission and use of satellite TV programs in the central, provincial capitals and municipalities directly under the Central Government. It can be used for radio stations and TV stations throughout the country. Organizations such as wireless transmitting stations and cable television networks provide high-quality, high-reliability uplink and ground receiving services for broadcast television programs. It can be seen from the coverage of the latter two satellites that the two are mutually supportive and have a different relationship. The 10 C-band transponders of Xinnuo No. 3 are limited to the domestic market. It is somewhat inappropriate for international channels like CCTV and some provincial-level satellite channels that are mainly publicized. Compared with before the turn-around, the signal The reduced coverage has made it impossible for Chinese audiences in the Asia Pacific region to receive programs. The coverage of Zhongxing 6B is very extensive, and it is equivalent to the pre-star. The 38 C-band high-power transponders on the star can not only meet the needs of domestic propaganda, but also provide strong support and guarantee for the future increase of satellite programs.
Different receiving objects
Zhongxing No.9 is a direct broadcast satellite dedicated to the “village to village†project, providing 48 sets of TV programs and some radio programs for remote and impoverished areas free of charge. The star adopts the direct transmission mode of the signal to the household. That is to say, the individual user only needs to install and use the satellite antenna and receiver with smaller aperture to directly hear the broadcast and receive the satellite program of the central and provincial provinces, which is especially suitable. Similar to the needs of the majority of herders in Inner Mongolia. Zhongxing 6B and Xinnuo No. 3 provide high-quality, high-reliability radio and television program uplink transmission and ground receiving services for broadcasting stations, TV stations, wireless transmitting stations and cable television networks throughout the country. From a technical point of view, the individual TV users on the two satellites can receive satellite radio and television programs smoothly with the corresponding receiving equipment. At present, in China, where cable TV is not widely available, some users receive TV programs through Zhongxing 6B and Xinnuo No. 3. What needs to be explained here is that Article 9 of the Regulations of the State Council of the People's Republic of China on the Administration of Ground Receiving Facilities for Satellite Television Broadcasting stipulates that: Individuals shall not install and use satellite ground receiving facilities. If there are special circumstances, if an individual really needs to install and use satellite ground receiving facilities and meet the licensing conditions stipulated by the administrative department of radio, film and television of the State Council, he must submit an application to his/her unit, and the newspapers and television administrative departments of the local county and municipal people's governments agree to report. The radio and television administrative departments of the people's governments of provinces, autonomous regions and municipalities directly under the Central Government shall examine and approve.
Different transmission systems used
Zhongxing 9 uses ABS-S (ADVANCEDBROADCASTSYSTEM-SATELLITE) independently developed by China. Zhongxing 6B and Xinnuo No. 3 adopt DVB-S (DIGITALVIDEOBROADCAST-SATELLITE). This determines that the receiving device must also use the corresponding standard to receive the signal. These two standards are essentially indistinguishable and are two implementations that are taken to achieve the same goal. The ABS-S standard is China's first satellite signal transmission standard with completely independent intellectual property rights. It has the advantages and characteristics of completely independent innovation, applicable feasibility and advanced security. In addition to its many advantages in terms of technology and adaptability, especially in terms of receiving performance, it is obviously superior to the current internationally accepted transmission standard. This standard is only used by China itself and is not compatible with the transmission standards adopted by overseas satellites. The user receives the overseas programs on other satellites to ensure the security of the satellite live broadcast system. On the other hand, choosing to ensure security means losing the possibility of receiving broadcast television signals from multiple satellites simultaneously with a single receiving device. The DVB-S standard is a satellite broadcasting standard currently adopted internationally. This standard is also adopted in most countries including China. The technology is very mature and the cost is low. It should be noted here that a satellite does not necessarily use only one transmission standard. For example, there are two sets of CCTV integrated channels in the TV program transmitted by Zhongxing No. 9, one of which adopts the DVB-S2 transmission system, right-handed circle In the form of polarization, the downlink frequency is 12180 MHz, and the symbol rate is 5632 KPBS. The satellite receiver using the ABS-S standard cannot receive the program, and only the receiver using the transmission system can receive the program. The DVB-S2 standard is a new generation of satellite transmission standards developed by the JTC (Joint Technical Committee), which is superior to the DVB-S standard in terms of service support, channel coding and modulation techniques and compatibility.
So there is already a mature DVB-S standard. Why did the China Star 9 satellite launched in June 2008 create another standard? The main reason is to avoid expensive licensing fees. For example, the manufacturer of each receiver must pay an expensive royalty tax to the MPEG organization for the sale of each component. China has about 400 million households. At the same time, the “village to village†project aims to make the majority of the rural population able to see digital satellite TV, which means that satellite TV must reduce costs.
Use frequency band and different receiving equipment
Users who watch the satellite TV program of Zhongxing 9 only need to use the 0.45-meter "small pot" antenna and the KU-band high-frequency head to receive clear radio and television signals. Zhongxing 6B and Xinnuo 3 use diameter. The signal is received by an antenna of 1.2 m or more and a C-band tuner. This is closely related to the frequency bands used by both. Zhongxing 9 uses the KU band, the KU band frequency is high, the satellite transponder has high power, the ground field strength is high, and the ground interference is small. It is very suitable for distributed small-caliber wireless individual reception, and adopts direct-to-home The way. However, there is a rain attenuation effect. The greater the rain, the greater the signal is affected. When severe, the signal will disappear. As a satellite program distribution service with very high reliability requirements, it is more powerful to use C-band transmission. Zhongxing 6B and Xinnuo No. 3 use C-band, C-band signal frequency is low, and the transmission power of satellite transponder is lower than that of KU-band. Therefore, using large-diameter antennas to receive, ground-wave signals will also form certain interference. As a user who receives the satellite radio and television program of Zhongxing 9th, pay special attention to the choice of antenna during installation. Generally, the 0.45-meter antenna can better prevent rain attenuation than the flat-panel antenna.
Different polarization modes
Zhongxing 9 uses circular polarization, while Zhongxing 6B and Xinnuo 3 use linear polarization. Circular polarization has several advantages over linear polarization:
The circularly polarized antenna is easy to adjust and is easy for users to receive TV signals.
Using a circularly polarized ground antenna, you can receive a satisfactory TV image signal by simply aiming at the satellite and adjusting the appropriate azimuth and elevation. The linear polarization method is used, and since the polarization angle of the antenna needs to be adjusted, the polarization angles of different regions are different, so the installation and debugging of the antenna is complicated.
It is easier to achieve dual-star synchronous orbit backup with circular polarization.
The same orbit is two linearly polarized satellites. If the initial polarization angle is inconsistent, it will not be able to achieve the same-frequency backup of the two satellites. It can only be a complete whole-star conversion. The use of circularly polarized two satellites with the same track backup can be backed up in a crossover manner, which is convenient for energy temperature management on the respective stars, so that the satellite is in a better working state.
Circular polarization is more suitable for mobile reception
China has a vast territory, a concentrated population in the east, scattered populations in the west, long coastlines, many islands and tens of thousands of kilometers of borders and tens of millions of herders, border guards, and other tens of thousands of moving vehicles. And the mobile population, it is suitable to receive TV programs with circularly polarized antennas.
Conclusion
All three satellites are resources of China Live Broadcasting Satellite Co., Ltd. One of the main tasks in the business application field is to complete the transmission and coverage of broadcast television signals, and the working principle is the same. The above is from the technical point of view, combined with users. The actual reception, the difference and analysis of some differences. At the same time, we also saw that the three satellites have a large space for development under the premise of fulfilling their mission, especially the satellite No. 9 of China Star.
Zhongxing 9 adopts live-to-home mode to broadcast TV signals for users free of charge. The user can receive signals smoothly in both fixed and mobile states with convenient receiving devices. There are 22 transponders on the star. Currently, only 4 are used. Transponders, the remaining 18 transponders are not in use. We can imagine that there is still a lot of room for development in the field of radio and television.
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