Abstract
Performance of a free space optical link can be improved by using polarization diversity. However, there is possibility of cross polarization induced crosstalk due to strong atmospheric turbulence. An analytical model for non Hermitian OFDM based DQPSK FSO system is developed to account for the cross polarization induced crosstalk in the presence of strong atmospheric turbulence. A closed-form expression of signal to noise plus crosstalk ratio and conditional BER for a given polarization misalignment and a given turbulence induced fading is derived. The average BER is evaluated by averaging the conditional BER over the pdf of the turbulence considering Gamma–Gamma distribution and Maxwellian distribution for random angular misalignment. Results are evaluated in terms of BER and receiver sensitivity improvement due to polarization diversity. The system power penalty for cross-polarization induced crosstalk in the presence of strong atmospheric turbulence is also found at a given BER. It is noticed that system BER performance degrades significantly and power penalty is found to almost 9.5dB, 12dB and 21dB for mean misalignment angle of 4°, 5°and 6°respectively at a BER of 10−8 and a given turbulence parameter Cn2=10−14m−2∕3 for a FSO link distance of 2000m. Finally, the analytical results with polarization diversity are compared with published results without diversity.
Published Version
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