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：本文研究了在滑动窗口最新时隙恢复框架下，基于正交频分复用的时分双工（TDD）系统的导频设计问题，该框架联合利用了最近时隙间的时延-多普勒稀疏性。在连续子带和公平性约束下，该视角自然引出了几何感知的时频联合导频分配。研究表明，有效的导频模式应在网格覆盖和冗余共线性抑制之间取得平衡，当无法完全消除共线性时，还需额外采用对称性规避优化。基于这些原则，我们构建了一种与实用TDD分配兼容的混合整数构造方法。数值结果表明，最小覆盖半径与共线性控制（MCC）模式在代理几何指标和最新时隙恢复性能方面均有提升。