| Satellite communications are used in a wide range of applications form military intelligence to weather forecast to commercial communications and entertainment. In special cases, satellite communication systems are required to perform with very low bit error rates. This requires the use of error coding techniques. In addition to that, in most cases satellite communication systems include nonlinear amplifiers to transmit from the satellite to the ground stations.;In this thesis, an analysis of the behavior of turbo coding in a nonlinear environment is presented. The relationship between coding gain and bit error rate at different power levels relative to saturation of a nonlinear amplifier is discussed. This analysis is performed using an end-to-end hardware platform. This hardware platform includes a digital modem, a radio frequency (RF) section, a nonlinear traveling wave tube amplifier (TWTA), and turbo coding ASIC. The analysis shows that coding gain is dependant on the power level of the nonlinear amplifier. In addition, the performance the 4+12 APSK modulation scheme on a nonlinear system using turbo coding is explored using a computer simulation of the hardware platform. The performance of the 4+12 ASPK modulation is compared to the performance of the 16QAM modulation scheme. The results show that the 4+12 APSK modulation scheme provides a better performance in a nonlinear system at low bit error rates. |
