DFT-Spread-Based OTFS Waveform Design With Good Peak-to-Average Power Ratio for Joint Sensing and Communications

We study the problem of orthogonal time frequency space (OTFS) waveform design for joint sensing and communications. Our main objective is to achieve a low peak-to-average power ratio (PAPR) for the OTFS waveform with DFT spread to communication symbols, so that good parameter estimation and bit error rate performances in the presence of phase noise can be obtained for the sensing and communication sides, respectively. To this end, we first devise a symbol pattern scheme with pilot and reference components elaborated in the delay-Doppler domain for the OTFS, with the aim of improving phase noise and channel estimations. Based on this, we then perform power allocations on the designed pattern to further implement the reduction of PAPR for the OTFS waveform. The overall OTFS design is formulated as an optimization problem that incorporates the PAPR metric into the objective function for minimization. By replacing the infinity norm with an equivalent form, we convert the formulated optimization problem into a new tractable form, which allows us to apply majorization-minimization techniques for finding solutions. Our major contributions also lie in elaborating the majorant for the resulting problem and transforming into its dual problem. Simulation results verify the effectiveness of our design.