Downlink Performance Analysis of Extremely Large-Scale MIMO-OFDM Systems for High-Speed Railway

Thepotential of extremely large-scale multiple-input multiple-output (XL-MIMO) systems to enhance the performance of high-speed railway (HSR) wireless networks is vast. In this correspondence, we examine the performance characteristics of the XL-MIMO-OFDM HSR system, focusing on uniform planar array (UPA) and uniform linear array (ULA) configurations. Considering the multipath spherical wave channel model, we develop a system model that accounts for the Doppler frequency offset (DFO) caused by train movement. Our analysis includes the performance of effective degrees of freedom (EDoF), deriving closed-form expressions for both UPA- and ULA-based systems. Additionally, we investigate the integration of XL-MIMO with orthogonal frequency-division multiplexing (OFDM), which enhances the signal-to-interference plus noise ratio (SINR) and spectral efficiency (SE) of individual base stations. Simulation results demonstrate the superior EDoF performance of UPA- and ULA-based XL-MIMO-OFDM systems. Moreover, the intercarrier interference resulting from train movement increases with speed, and the degradation in signal quality caused by this interference can be mitigated by configuring the XL-MIMO-OFDM system. Notably, the adoption of XL-MIMO technology with a near-field channel model significantly improves coverage reliability compared to traditional MIMO configurations using a far-field channel model.