Coding and Modulation

The modulation scheme chosen for this experiment will be QPSK. This modulation scheme is commonly used in satellite communication systems. Considering the fact that the satellite will be traveling in the GEO region, the distance is 36768km, significant path loss will occur, thus making it difficult to use APSK modulation. With the C/N given by the link budget will be approximately 36dB. The rain attenuation assuming horizontal polarization with a precipitation rate of 95mm/hr would be 14.7 dB at an effective length of 1km. This calculation is based on an extrapolation of the k and α coefficient for the southeast region. In order to mitigate the effects of rain fade or other interference and propagation problems we will use turbo code (120,240) to obtain a coding gain, which will reduce the C/N required by 4db to reach a bit error rate found without coding.

Rain Attenuation Equation:

Where A is the attenuation in dB, γR is the specific attenuation, k(0.8025) and α(0.64) are constants based on frequency(75GHZ) and R is the rain rate in mm/hr.