Mitigation Techniques for FSO
Environmental conditions create significant obstructions to completing satellite-to-ground links (SGL) with OGSs. Multiple potential approaches exist to negate environmental effects and maximize transmission efficiency. Those approaches may be considered in two basic categories:
- Methods to improve the reliably of the FSO link
- Methods to bypass a faulty link in favor of a reliable alternate link.
The performance of Free Space Optics (FSO) depends on various parameters such as number of subcarriers, base band modulation, nature of laser beam, turbulence modeling, and much more. Various diversity techniques have been studied by researchers for the improvement of signal strength due to fading caused by atmospheric turbulence. A novel channel coding scheme formed by serially concatenation of irregular low-density parity check (LDPC) and trellis coded modulation (TCM) codes linked by interleaver was proposed by Gupta et al. The proposed unified coding scheme was simulated and analyzed using the lognormal scintillation model, which is suitable for weak turbulent conditions. The obtained results are the comparative study of various channel coding schemes in terms of bit error rate (BER) vs. signal-to-noise ratio (SNR). Simulation results confirmed newly designed hybrid code outperformed the independently coded and uncoded systems under weak turbulence conditions by reducing the number of errors in the transmitted information that occurs due to fading. It is found that the presented hybrid coded OFDM-FSO system with 16-level quadrature amplitude modulation (QAM) provides significant improvement with less decoding complexity and reasonable delay.