Reliable equalization aided long-distance OFDM-FSO performance analysis over Gamma-Gamma turbulence with thermal and...

Free Space Optical Orthogonal Frequency Division Multiplexing (FSO- OFDM) has emerged as a powerful distinct transmission framework for next-generation wireless links; here the performance of FSO system using OFDM in Low Earth Orbit/Medium Earth Orbit (LEO/MEO) inter-satellite communication is investigated under the combined effects of thermal, background noise and solar storm disturbances over a Gamma-Gamma (GG) channel model. An impact of channel impairments are analysed for BPSK, QPSK and M-ary (M = 64,128,256) QAM transmission. A bit error rate in the received signal is analysed for different refractive index with weak and strong turbulence conditions. To increase the transmission link distance and reduce the bit error rate, we employed zero forcing equalization techniques at the receiver. We examine the different transmission channel length from 1000 to 11000 m. Lower order PSK modulation schemes such as BPSK and QPSK indorse reliable performance for link ranges up to 7000 m due to their robustness to turbulence and noise. The simulation results substantiate that in weak turbulence OFDM-FSO system, 256-QAM achieves high spectral efficiency with a BERvalue of 10^-12 at 23 dB SNR. Under severe turbulence, BPSK is optimal up to 7000 m with a BERof 10^-12 at 22 dB SNRin weak, and 27 dB in strong turbulence, whereas for long distance up to 11000 m, 256-QAM becomes more efficient, reaching a BERof 10^-6 at 27.5 dB SNR. The analysis further demonstrate that for an identical symbol rate, the BER achieved at 11000 m in weak turbulence closely bouts the BER obtained at 9000 m when the channel experiences strong turbulence like solar storm. Furthermore, the developed equalization framework exhibits superior performance compared to traditional attitudes, demonstrating its capability to sustain stable long-range OFDM-FSO communication for LEO/MEO inter-satellite links.