Performance analysis of a two-channel polarization division multiplexed optical DQPSK FSO link with the effect of atmospheric turbulence

摘要

Polarization division multiplexing (PDM) is a promising technique to increase the capacity of future free-space optical (FSO) system due to availability of optical PDM multiplexer/demultiplexer. However, there are limitations due to cross-polarization-induced crosstalk and atmospheric turbulence. A novel analytical model of a DQPSK PDM FSO link is analyzed in this paper to determine the deterioration in error rate performance considering the cross-polarization-induced crosstalk in the presence of atmospheric turbulence. A closed-form expression for signal-to-crosstalk plus noise ratio and bit error rate conditioned on a given turbulence-induced fading and a given angular misalignment due to cross-polarization at the output of optical PDM DQPSK receiver is derived. By averaging the conditional BER, the average BER is found over the probability density function of the turbulence considering a log-normal distribution and random angular misalignment which is considered to have a Maxwellian distribution. The results are given in terms of BER and system power penalty because of cross-polarization-induced crosstalk with the effect of weak atmospheric turbulence. It is noticed that system BER performance degrades significantly and power penalty is found to almost 8.2 dB, 9.2 dB and 12 dB for mean misalignment angle of 4°, 5° and 6°, respectively, at a BER of 10~(-10) and a given turbulence parameter C_n~2 = 10~(-14)m~(-2/3). Finally, our analytical work is verified with others earlier published work.