A Non-Stationary Channel Model for Aerial Intelligent Reflecting Surface With 3D Continuously Arbitrary Trajectory

Nan Ma, Shaoyi Liu, Jianqiao Chen, Xiaoqi Qin, Ke Peng, Kaiheng Zhang

Abstract: Intelligent reflecting surface (IRS) is considered as one of the revolutionary technologies for sixth-generation (6G) wireless communication as it can be adapted to assist communication systems by adaptively manipulating the propagation environment and greatly expanding network coverage. In this case, the aerial IRS (AIRS)-assisted communications have unique advantages, such as more flexible deployment and wider service coverage. However, accurate channel modeling of AIRS-assisted system is challenging due to mobility. In this paper, we propose a novel geometry-based three-dimensional (3D) wideband channel model for AIRS-assisted multiple-input multiple-output (MIMO) communication systems, where the rotational degrees of freedom in three directions and the arbitrary trajectory of AIRS in space are specially considered. Firstly, a novel geometry-based 3D channel model that considers the realistic motion trajectory of UAVs in reality is proposed. The scatterers in the environment are modeled as different clusters set to simulate the frequency-selective fading caused by multipath effects. Secondly, a space-time-related cluster visibility algorithm based on the birth-death process is developed to characterize the non-stationarity introduced by the mobility of AIRS. Based on the model, the channel impulse responses (CIRs) and the corresponding statistical characteristic functions are derived. Finally, we investigate and analyze the impacts of different AIRS trajectories on channel statistical characteristics, such as the space-time correlation function, Doppler power spectral density, and channel capacity. Meanwhile, the influence of non-ideal AIRS on the channel is discussed, including discrete phase design and discrete time reflection phase. Simulation results demonstrate that the proposed model can accurately capture the channel properties, which therefore provides valuable insights for future development of AIRS for 6G systems.