Performance of multilevel differential polarization shift keying with estimation of inclined polarization axes over atmospheric turbulence channel

Multilevel polarization shift keying (MPolSK) is an optical modulation scheme, in which the state of polarization changes according to transmission data. When either the transmitter or the receiver is not fixed, the mismatched polarization axes is caused. It significantly degrades the communication performance. To overcome this problem multilevel differential PolSK (MDPolSK) was proposed, in which we perform differential encoding on a pair of successive transmission symbols. Because the decoding process needs two successive symbols and they are affected by independent noises, MDPolSK is sensitive to noises. In this paper, to reduce the noise influence in MDPolSK, we propose a method to estimate the inclined polarization axes. By using the estimation method the symbol error rate (SER) of MDPolSK can approach that of MPolSK, even in the case of the mismatched polarization axes. In addition, we study the intensity fluctuation caused by the atmospheric turbulence channel and show its influence on the SER of MDPolSK. The intensity fluctuation is modeled by the lognormal distribution.