Block-wise digital signal processing for polmux QAM/PSK optical coherent systems

In polarization multiplexing based coherent optical transmission, two main kinds of impairments have to be counter-acted: 1) the inter-symbol interference generated by the chromatic dispersion and the polarization mode dispersion and 2) the frequency offset. Usually adaptive approaches are carried out to mitigate them. Since the channel is very slowly time-varying, we propose to combat these impairements by using block-wise methods. Therefore, we introduce two new algorithms: the first one is a block-wise version of blind time equalizer (such as CMA), and the second one estimates the frequency offset in block-wise way. These algorithms are suitable for PSK and QAM constellations. By simulation investigations, we show that they outperform the standard approach in terms of convergence speed only at a moderate expense of computational load. We also experimentally evaluate their performance using 8-PSK real data traces and off-line processing which takes into account other physical impairments such as phase noise and non-linear effects.