Recently, OFDM systems have been proposed as a solution to solve broadband railway communication problems. Channel estimation and equalisation for OFDM system become challenging when the mobile terminal is moving at high speed as the OFDM subcarriers lose their orthogonality in such situations. In this paper we present a novel channel estimation algorithm based on the hyperbolic modelling of rapidly varying channels. The hyperbolic model is based on the observation of the OFDM frequency domain channel matrix provided by rapid channel simulator, and on mathematical analysis of the off-diagonal elements of the channel matrix. The hyperbolic model can be combined with an FFT interpolation technique and then used to perform an iterative least square estimation of the channel matrix even when sparse pilot distribution is used. Furthermore, a sliding window discrete optimisation procedure is introduced to improve the performance of the suboptimal Linear Minimum Mean Square (LMMSE) channel equalisation technique. Numerical results for a mobile moving at 280 km/h and under the Wide Sense Stationary Uncorrelated Scattering (WSSUS) channel assumption are reported. The provided results prove the efficiency and effectiveness of the suggested algorithms.
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机译：近来，已经提出了OFDM系统作为解决宽带铁路通信问题的解决方案。当移动终端高速移动时，OFDM系统的信道估计和均衡变得具有挑战性，因为在这种情况下，OFDM子载波失去了正交性。在本文中，我们提出了一种基于快速变化通道的双曲线建模的新颖通道估计算法。双曲模型基于对快速信道模拟器提供的OFDM频域信道矩阵的观察，以及对信道矩阵的非对角线元素的数学分析。双曲模型可以与FFT插值技术结合使用，然后即使在使用稀疏导频分布的情况下，也可以用于执行信道矩阵的迭代最小二乘估计。此外，引入了滑动窗口离散优化程序以改善次优线性最小均方（LMMSE）信道均衡技术的性能。报告了移动速度为280 km / h且在宽感平稳不相关散射（WSSUS）信道假设下的移动台的数值结果。提供的结果证明了所提出算法的有效性和有效性。
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