Given the high transmission loss, severe Doppler spread and large multipath delay in the underwater acoustic (UWA) channel, the channel estimation and tracking in the conventional orthogonal frequency division multiplexing (OFDM) based UWA systems are severely unaffordable. In this paper, we propose a low-complexity and cost-friendly OFDM-based differential cyclic-shifted differential chaos shift keying (OFDM-DCS-DCSK) system which offers a high data rate, superior robustness and enhanced system security for UWA communications without the need for channel state information (CSI). In the system, the information bits are carried by different step lengths of the cyclic shifts. At the receiver, a low-complexity detection method is used to search the position of maximum from the cyclic correlation values and therefore estimate the information bits. Finally, simulation results demonstrate the proposed OFDM-DCS-DCSK system outperforms its competitors both in bit error rate (BER) performance and in system security.

Redirected walking allows users to walk naturally through a large immersive virtual environment while the physical space is limited. Previous studies have analyzed human sensitivity to redirected walking in a horizontal direction, but users also need to walk on slopes to change their height. In this work, we expand the vertical movement space by positioning users on virtual paths with slopes that are different from those of real paths. We conduct psychological experiments to explore human sensitivity to slope gains that describe the discrepancies between the slopes of paths in virtual and real environments. The investigation shows that humans can walk on virtual slopes that are higher or lower than the real position without detecting the slopes and establishes corresponding detection thresholds.