Comparative performance analysis between STBC and SFBC on a non-Hermitian OFDM free-space optical system with polarization diversity

摘要

In this paper, we proposed an analytical model for a non-Hermitian orthogonal frequency division modulation system considering space time block coding (STBC) with polarization diversity in presence of strong atmospheric turbulence and compare the bit error rate (BER) performance with the same system considering space frequency block coding (SFBC). We developed this analytical model to calculate the impact of crosstalk and fading on system performance due to cross polarization and strong atmospheric turbulence respectively. The analytical expressions for signal to noise plus crosstalk ratio are derived for a certain amount of random misalignment angle. We consider two different independent probability density functions one is Maxwellian distribution and another is Gamma-Gamma distribution for angular misalignment and strong turbulence respectively. The average BER is found by averaging the conditional BER over this two probability density functions. It is noticed that, receiver sensitivity improvement due to STBC coding is almost 4.5 dB at a BER of 10(-12) compare to 7.5 dB due to SFBC coding reported earlier by the authors. From the analytical results, we clearly found that SFBC coding performs better than STBC coding for the same system's constraints. Finally, results of our proposed work are verified with others earlier published results and it is found that our result is almost 2 dB better than the published results.