Optimization of 4-Dimensional Modulation and Coherent Receiver Processing in Optical 28-Giga-Baud Lab Transmission System

Summary: Today 100-Gbit/s optical transmission systems are based on coherent detection of the transmitted optical carrier which is independently phase and amplitude modulated in two orthogonal polarizations at a symbol rate of 28-Gbaud. Digital signal processing (DSP) algorithms implemented in receiver ASIC perform adaptive demultiplexing, distortion equalization, and phase estimation of the detected optical signal as well as error-correcting decoding if channel coding is applied.

In frame of the Master thesis a coherent receiver DSP algorithm shall be refined for processing of 4-dimensional (4D) modulated signals. Specifically receiver phase, frequency estimation and butterfly FIR filter shall be extended to full 4D operation and nonlinear filtering such as decision feedback equalization shall be developed and implemented. Performance shall be numerically analyzed by simulation and by application of measurement data which have to be generated by experiment regime of the fiber shall be evaluated.

Soft-decision error correction tailored to 4D formats, which are provided by Bell Labs, Alcatel-Lucent, shall be implemented in the receiver algorithm and the operation -joint with other processing- shall be investigated. Specifically the tradeoff between constellation order rates shall be discussed.

Moreover, different existing options of 4D modulation formats (POLQAM) shall be evaluated the 32, 64 and more point constellations shall be optimized by Sphere Packing algorithm, Densest Lattice Packing algorithm or other methods. The method should also be extended to a higher dimensional modulation. Attention should be paid to the optimization of bit mapping to constellations points in view of efficient error correction decoding using heuristic (Ant Colony Optimization) and other algorithm.