The Major Concern in Design and Analysis of Satellite Link

Satellite links are used to deliver long distance telecommunications such as voice or data services, broadband internet services, television broadcast and communications with remote and hard to reach locations. Satellite link consists of an uplink and a downlink. Uplink connects ground station to satellite while downlink connects satellite to the receive ground station. Signal quality in the uplink depends on how powerful the signal is transmitted from the source ground station and how the satellite receives it. On the downlink side, signal quality depends on how powerful the satellite retransmits the signal and how the ground station receives it.

The main purpose of satellite link design is to maximize link data rate while reducing the BER (Bit Error Rate) at the receiver subjects to the constraint of received power and channel bandwidth. The BER of a satellite link is a function of Eb/No, which means energy per bit noise density ratio in the information channel. A satellite communications system designer must ensure a minimum Eb/No in the receiver channels to satisfy the link BER criteria which also meet the constraints on satellite transmit power and RF bandwidth. In digital transmission, Eb/No in a baseband channel relies on C/N (carrier to noise ratio) of the receiver, the type of modulation used in the baseband channel and the channel bandwidth. Hence, the major concern in design and analysis of satellite link is to calculate and evaluate the link C/N in which C is the received carrier power in the earth station/satellite and N is the noise plus interference (caused by earth stations of adjacent satellite) power in the receiver.

Rain is the major destruction of satellite signal. Rain attenuation is a function of rain rate at ground station location and satellite link carrier frequency. Average charge of rain rate (mm/hr) of a country can be obtained from the department of Meteorology of that country. Rain effects become stern at wavelength approach the rain drop size. So you have to ensure that the satellite link can overcome the maximum attenuation induced by the rain. Hence, accurate assessment needs to have evaluating link parameters.