Affect Satellite Digital Video Broadcast Signal Transmission Main Factors - Satellite, Digital Video

Of: Guangdong Mr Chan, Satellite digital TV with a large coverage area

, transmission of high quality, saving advantages of satellite resources and improve radio and television coverage of the population, a strong impetus to the development of radio and television career. Although satellite digital video broadcasting has many advantages, but the signal transmission is also subject to certain factors, such as natural phenomena, the satellite signal interference between the uplink and downlink transmission system to accept the imperfect system resulting from the impact. Following on the impact of satellite digital video broadcasting (DVB-S) were the main factors of signal transmission to be introduced.

Natural phenomena Satellite digital video broadcasting system is an open communication system, its transmission link is susceptible to the influence of external natural conditions, such as rain, snow days Ling, ionospheric scintillation, solar magnetic storms and so on.

1, the impact of rainfall When the waves through the rain area, rain will generate absorption and scattering of waves, resulting in attenuation, referred to as rain attenuation. Rain attenuation depends on the diameter of raindrops and the wavelength of electromagnetic wave, electromagnetic wave of wavelength and attenuation of rain closer to the larger diameter. Experimental results show that the radius of raindrops between about 0.025 ~ 0.3cm, in the Ku-band, the wave of wavelength about 2.5cm, so Ku-band rain attenuation effect is larger; in C-band, because the wavelength of 7.5 cm, the wavelength is greater than the radius of rain, so rain attenuation is relatively small. Rain attenuation of electromagnetic waves not only, but also the noise caused by temperature increase and the occurrence of depolarization affect the received signal carrier to noise ratio and lead to interference between orthogonally polarized signals increased.

Cloud attenuation caused by rain attenuation is much smaller than that, but to receive Ku band signals for the small caliber of the terminal, which may have been exceeded or the margin between the receiving device.

2, the impact of snow General, unless it is snow, snow and below on the Ku-band satellite signal will not produce significant attenuation (not too thick snow on the feed), but in the process of snow, for the C-band and Ku band satellite transmission, the impact is very significant. Of snow in the process, the antenna feed and main reflector produces uneven snow on the strength of electromagnetic scattering and absorption of different, serious damage to the satellite antenna aperture field uniformity of the distribution function, greatly reduces the gain of the antenna also increases the antenna noise temperature, the uplink EIRP values or receiving system G / T values will be greatly reduced, affecting the transmission quality of the satellite signal. As the snow continued normally Naturalization longer, the gain of the antenna significantly affected, so both the uplink station or downlink stations are required to have taken active measures to prevent and overcome.

3, on the phenomenon of Ling Before and after each equinox and autumnal equinox

, satellite earth stations located around noon every day, the satellite will be in a straight line between the Sun and the Earth. Then satellite earth station antenna in satellite also aimed at the sun (as shown in Figure 1), so that strong electromagnetic waves generated by the sun directly shining on the earth station antenna. Since the sun produces a wide spectrum of electromagnetic waves, so the Earth station for the electromagnetic wave is a large noise source, it will interfere with receiving the satellite signal receiver chain so that the serious deterioration or even interrupted, a phenomenon that is as satellite communications, "Japanese Ling phenomenon."

Figure 1 Ling day on the duration of the earth station by the decision of the receiving antenna aperture, the greater the receiving antenna aperture, Japan Ling relatively short duration; the other hand, the smaller diameter antenna, the longer the duration. Ling on the received signal to noise ratio on the impact of noise depends on the size of the sun, the operating frequency band width and height. Ling peak of solar activity interference due date the most serious; work the more wide-band noise before the more interference is relatively serious; work the higher the frequency, the greater the noise intensity, for example: Ku-band satellite signal interference by the day is greater than C Ling band seriously. Ling in the day time, solar energy for heating also enables high-frequency antenna feed before the first case temperature, the necessary measures be taken to protect it.

4, the phenomenon of ionospheric scintillation

When the waves travel through the ionosphere, due to the uneven structure of the ionosphere and the random time variation, resulting in signal amplitude, phase, angle of arrival and other characteristics of short-period changes in the formation of ionospheric scintillation. Ionospheric scintillation and frequency, geographical location and solar activity status. In general, ionospheric scintillation in the spring equinox occurs when the most serious around, the more serious after the autumnal equinox. Ionospheric scintillation phenomena usually last 30 minutes to several hours, usually occurs after sunset (18:00) to midnight (24:00) end. Although the ionospheric scintillation 3GHz frequency mainly in the following, but there was a marked effect 4GHz. According to ITU statistics, 4GHz, ionospheric scintillation can cause changes of more than 10dB peak to peak.

On Earth there are two more serious ionospheric scintillation region: 20 degrees within the magnetic equator and high latitudes. China's Yangtze River and south of the Yangtze River to the north of the ionosphere in parts belong to the peak of activity areas (see Figure 2), ionospheric scintillation phenomena in the region before and after the spring equinox and the autumnal equinox is very obvious in the performance of 4GHz, the peak more than 10 dB, but Under normal circumstances, although the cause of ionospheric scintillation signal quality decreased, and will not cause circuit interruption.

Figure II 5, the phenomenon of solar magnetic storms

Frequent in recent years, a strong solar flare on Earth communications facilities will therefore be part of the interference. Accompanied with the flares, the sun's surface will produce a powerful coronal mass ejection, jet stream of charged particles produced after the earth's magnetic field may form a relatively strong geomagnetic storms, satellite operations and communications, interfere with, or even serious will interrupt the satellite signal.

by: gaga

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