✍ Scribed by Cusani, Roberto ;Baccarelli, Enzo ;Galli, Stefano
No coin nor oath required. For personal study only.
A new procedure is proposed for estimating the State‐of‐Polarisation of the received optical signal in Four‐Quadrature Amplitude Modulation systems. The proposed solution, which is obtained on the basis of the Maximum Likelihood criterion, is merely electronic and operates in the presence of laser phase noise, photodetection noise and cross‐polarisation interference. It employs a suitably designed training sequence to estimate Jones' parameters in the data‐aided training mode. A proper decision‐directed procedure is then activated to lock‐in the estimated parameters in the operative mode. The variances of the resulting estimation errors are evaluated and the overall system performance is given in terms of Bit Error Probability versus signal‐to‐noise ratio. The theoretical analysis and the computer simulations show the superiority of the proposed recovery procedure with respect to alternative solutions recently proposed in literature.
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