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Orthogonal time frequency space (OTFS) modulation has shown its advantages in high-mobility scenarios compared to orthogonal frequency division multiplexing. In this work, we focus on the OTFS pilot design and optimization from the perspective of improving the spectrum efficiency without degrading the channel estimation and symbol detection performance. We first propose a novel pilot pattern, where the proportion of guard symbols is reduced. To achieve accurate channel estimation, based on the average mutual incoherence property criterion, we further formulate an OTFS pilot sequence optimization problem and develop a particle swarm optimization (PSO)-based algorithm for solving it. Later on, a simple yet effective interference cancellation scheme is adopted to address the pilot contamination in the proposed pilot pattern. Our simulation results show that the optimized pilot sequence significantly …