Constantly increasing demand for wireless communications in various applications has always led to new ways of modulating the radio frequency (RF) carrier signal by advancing waveform structure throughout generations. Although communication data rates are limited by the theoretical capacity, specific signaling designs for the signal that experiences natural and artificial effects in the transmission medium such as multipath fading channel, hardware impairments and multiuser environment promised better solutions in providing improved wireless access to various type of users and networks. Besides communication capacity, broadcasting nature of radio signals poses the information security as another main concern in wireless communications. In this dissertation, new advanced methods for improving signal statistics in multiple domains are studied. Instead of focusing on a single aspect, the waveform design approaches studied in this dissertation tackle with improving the orthogonal frequency-division multiplexing (OFDM)-based signaling in multiple perspectives such as out-of-band (OOB) emission reduction, peak-to-average-power ratio (PAPR) reduction, and secure transmission with minimum or no eect at the receiver side. Various concepts are coherently exploited while achieving aforementioned goals with minimal cost such as unexplored spaces in the signal space like (CP), guard band, multipath fading; multivariate nature of the multicarrier signals; time spreading and location uniqueness of the wireless channels. The proposed techniques are analyzed theoretically and performance results are presented including related previous works in the literature. It is worth noting that the methods presented in the dissertation can be easily applicable to conventional OFDM systems thanks to having no or minimal change in the receiver structure.