This study investigates the performance of scintillation mitigation for linear polarization shift on-off keying (LPS-OOK) transmission in free-space optical (FSO) communications. Scintillation effect is a critical issue for FSO communication in vertical links. The LPS-OOK signal with orthogonal linear x- and y-polarizations for bits '1' and '0' is modulated and transmitted from the transmitter end. The bits '1' and '0' suffer the scintillation effect in turbulence channel. Based on the orthogonal polarization characteristics of LPS-OOK, linear polarizer (LP) is used to mitigate the scintillation effect on bit '0' by blocking its polarization without the distortion of bit '1'. Further, owing to the nonlinear gain characteristics of logarithmic amplification, it is used to equalize the intensity fluctuation of bit '1'. Finally, the equalized LPS-OOK is distinguished using fixed threshold decision (FTD) instead of a complex symbol-by-symbol estimation of adaptive threshold. The performance of the proposed technique was verified experimentally for various degrees of the turbulence channel. A Mach-Zehnder modulator (MZM)-based turbulence channel simulator was adopted to accommodate turbulence-induced scintillation effect. The experimental results confirmed that the proposed technique that employed FTD has an improved bit-error-rate (BER) performance compared with that of OOK that employed an adaptive threshold decision (ATD) under various degrees of turbulence channels.
Bibliographical noteFunding Information:
This work was supported by the Institute for Information & Communications Technology Promotion (IITP) funded by the Korea Government through the Ministry of Science and ICT (MSIT) (Free Space Optical Communication Based Vertical Mobile Network) under Grant 2019-0-00685.
All Science Journal Classification (ASJC) codes
- Computer Science(all)
- Materials Science(all)