Satellite links are used to provide telecommunications voice/data services, broadband Internet services, television broadcasts, and communications with remote and hard-to-reach locations. The satellite link consists of an uplink and a downlink. The uplink connects the transmitting earth station to the satellite and the downlink connects the satellite to the receiving earth station. The quality of the signal in the uplink depends on the strength of the signal transmitted from the source station and how the satellite receives it. On the downlink side, the signal quality depends on the strength of the satellite retransmission signal and how the radio receives the signal.
Earth stations are classified by their antenna size. Large stations have an antenna diameter of 10 to 30 meters. The antenna of the small station is between 1 and 10 meters in diameter. The VSAT [very small aperture terminal] has an antenna with a diameter of 0.3 to 1 meter. When designing a satellite link, three earth station system parameters need to be considered. The first is the transmitter EIRP [effective isotropic radiated power], which is equal to from
platinum from
[transmitter output power] multiplied by from
GT from
[transmit antenna gain]. The EIRP measures the signal power emitted from the transmitting earth station. The second parameter is the quality factor is equal to from
G from
[receiver antenna gain] divided by from
Ť from
[system noise temperature]. from
G / T. from
Measure the sensitivity of the receiving system and the quality of the received signal. The third parameter is the system noise temperature, which measures the noise power generated by the receiving earth station.
The main purpose of the satellite link design is to maximize the link data rate while minimizing the BER [bit error rate] of the receiver body to achieve constraints on received power and channel bandwidth. The BER of the satellite link is a function from
Eb / No. from
[per bit noise density ratio in the information channel]. Satellite communication system designers must do their best to ensure a minimum from
Eb / No. from
The link BER standard is met in the receiver channel, which also satisfies the limits of satellite transmit power and RF bandwidth. In digital transmission, from
Eb / No. from
Depends on the baseband channel from
C / N. from
[carrier-to-noise ratio of the receiver], the modulation type and channel bandwidth used in the baseband channel. Here, the main focus of satellite link design and analysis is to calculate and evaluate links. from
C / N. from
In which from
C from
Is the carrier power received by the earth station/satellite from
n from
It is the noise plus interference [caused by the earth station of an adjacent satellite] in the receiver.
Rainwater loss is the most important shortcoming of satellite signal transmission. Rain attenuation is a function of the rainfall rate at the earth station location and the carrier frequency of the satellite link. The average of a country's rainfall rate [mm / hr] can be obtained from the country's meteorological department. The rainfall effect becomes different when the wavelength is close to the size of the raindrop. If the satellite link is to be maintained during rain, additional transmit power is required to exceed the maximum attenuation due to rain. When assessing link parameters, an accurate assessment of the expected rainfall is required.
The earth station antenna viewing angle [azimuth and elevation] can be calculated using the longitude of the geosynchronous satellite plus the latitude and longitude of the earth station. The deviation of the antenna pointing direction from the antenna axis is called the antenna pointing error. This error reduces the gain of the earth station antenna because the antenna gain is greatest when measured on its electrical axis. Here, antenna point loss needs to be evaluated in the satellite link design, and it is suitable for transmitting and receiving antennas.
Orignal From: Satellite link design considerations
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