The continuous increase of the worldwide data traffic demands new concepts for data transmission in the optical fiber-based backbone networks. One promising way to increase the capacity of the existing fiber infrastructure is to use quadrature amplitude modulation (QAM) in combination with polarization-multiplexing and coherent detection. In this book all necessary algorithms are presented that are required for the realization of such a system using digital signal processing at the receiver. The main focus thereby lies on the algorithms for polarization control and carrier recovery. But also...