On the influence of mobility: Doppler spread and fading analysis in rapidly time-varying channels

This paper focuses on the influence of mobility in rapidly time-varying channels. Local and global behaviors are researched based on the path-based channel model and ray-tracing channel model, respectively. The scenario employed in the global behavior analysis is a realistic composite high-speed railway (HSR) scenario, which is reconstructed by SketchUp. The analysis results include frequency modulation parameters caused by the Doppler spread and level crossing rates (LCR) indicating the occurrence rate of fading dips. The almost fixed frequency modulation is observed in the scenario with single-direction scatterer distribution and/or strong LOS path existing, and it is accompanied with lower LCR. The speed of mobility determines the “zoom” scale of characteristic curves in both time and frequency domain in a continuous scenario for the same starting point. The results are applicable to the design of high-speed railway wireless communication systems and the Doppler compensation of the various Doppler spread channels.

I. Introduction

The advance of intelligent transportation systems (ITS) has already attracted extensive attention from both research community and industry [1]. As the main way of information transmission, the wireless communication system is an essential element in the ITS development. The deep understanding of rapidly time-varying channels is an important prerequisite to developing effective and reliable communication systems. The rapidly time-varying channel is basically caused by the fact that the mobile station (MS) with high mobility has experienced different propagation environments over a short time frame. The high mobility directly leads to the Doppler spread and fading in frequency and time domain, respectively [2]. Thus, the analysis on the effects of mobility on Doppler spread and fading, which is combined with the geometry information of the propagation environment, is required.