This letter studies pilot design for orthogonal frequency-division multiplexing-based time-division duplex (TDD) systems under a sliding-window latest-slot recovery framework that jointly exploits delay-Doppler sparsity across recent slots. Under contiguous-subband and fairness constraints, this viewpoint naturally leads to a geometry-aware time-frequency joint pilot assignment. We show that effective patterns should balance grid coverage and redundant-collinearity suppression, with an additional symmetry-avoidance refinement when complete collinearity elimination is infeasible. Based on these principles, we formulate a mixed-integer construction method compatible with practical TDD allocation. Numerical results show that minimum-coverage-radius and collinearity-control (MCC) pattern improves both surrogate geometry metrics and latest-slot recovery performance.

翻译：本文针对基于正交频分复用的时分双工（TDD）系统，在滑动窗口最新时隙恢复框架下研究导频设计问题，该框架联合利用最近时隙间的时延-多普勒稀疏性。在连续子带和公平性约束下，该视角自然引出一类几何感知的时频联合导频分配方案。研究表明，有效导频模式需平衡网格覆盖与冗余共线性抑制，当完全消除共线性不可行时，需额外进行对称规避优化。基于上述原理，我们构建了兼容实际TDD分配的混合整数规划方法。数值结果表明，最小覆盖半径与共线性控制（MCC）模式既能改善替代几何指标，又能提升最新时隙恢复性能。