Gkeralnto Balla

This thesis investigates the Orthogonal Time Frequency Space (OTFS) modulation and its implementation in high mobility telecommunication systems. The OTFS waveform proves to be exceptionally robust in doubly dispersive channels. By utilizing the Symplectic Finite Fourier Transform (ISFFT/SFFT), it spreads the signal’s energy across both time and frequency domains, thus providing a massive degree of diversity against high Doppler conditions. However, the waveform suffers from a high Peak-to-Average Power Ratio (PAPR), which leads to signal distortion caused by power amplifier nonlinearities.

In the first part, the application of OTFS modulation with Pinching Antenna Systems (PASS) is proposed and studied, aiming to provide seamless connectivity for high-speed trains inside tunnels. An analytical mathematical model of the OTFS-PASS channel with fractional delays and Doppler shifts is developed. Asymptotic capacity bounds are derived, and extensive simulations demonstrate the clear superiority of OTFS over OFDM, which breaks down under high mobility conditions due to inter-carrier interference. Finally, it is revealed that OTFS suffers from a high Peak-to-Average Power Ratio (PAPR), which leads to signal distortion caused from power amplifier nonlinearities.

To address this issue, the second part of the thesis analyzes the PAPR of OTFS and proposes a novel Constant Envelope OTFS (CE-OTFS) modulation technique. By mapping the information onto the phase of the signal, this technique mathematically guarantees a unitary PAPR. The bit error probability over an AWGN channel is derived analytically, revealing the theoretical performance bounds imposed by the phase wrapping phenomenon.