Analytical Performance Evaluation of a STBC Coded OFDM FSO Communication System over Turbulent Atmospheric Channel

Resumo

An analytical approach is presented for an optical IM/DD system with STBC coded OFDM RF subcarrier modulation over a free space optical turbulent channel. The analysis is developed to find the expressions for the output photodetector current and carrier to noise power ratio at the output of the STBC–OFDM demodulator. The average bit error rate is evaluated numerically considering log-normal distribution of the atmospheric turbulence. The numerical results show that STBC-OFDM optical link suffers power penalty due to atmospheric turbulence significantly. However, the power penalty can be reduced by increasing the number of OFDM subcarriers. For example, power penalty for (2X1) STBC with N = 16 OFDM subcarriers is 7.5 dB and the power penalty reduces to 0.55 dB when N is increased to 64. Results are evaluated for different link distance, OFDM subcarriers and various channel condition.