*Dissertation Advisor: Dimitris Syvridis, Professor Advanced modulation schemes and signal processing techniques for transmission in highly multimode fibers

In this dissertation, advanced modulation schemes and digital signal processing techniques are proposed and investigated through both numerical simulations as well as experiments, in order to overcome the limitations of multimode step index plastic optical fibers (SI-POF) to support data rates in the order of Gbps. In particular, novel multi-carrier modulation techniques with the inherent property of symbol spreading (spreading multicarrier modulation schemes) are proposed and applied. These schemes are Discrete Fourier Transform Spread Discrete Multitone (DFT-Spread DMT) and Code Division Multiple Access Discrete Multitone (CDMA-DMT), which, in this thesis, are suitably adapted for short-range IM/DD transmission via SI-POF and compared against conventional Discrete Multitone (DMT) in terms of achieved transmission rate given a target bit error rate. Evaluation is performed for links of 50m and 100m by exploring various cases affecting the overall performance, including rate adaptation and artificial PAPR reduction. In all cases it is found that the DFT-spread DMT perfoms better than all other schemes, followed by CDMA-DMT hence, paving the way for more elaborated research for optimizing its transmission properties.