Geometry-Based UAV-MIMO Channel Model for Intelligent Reflecting Surface-Assisted Communication Systems

A geometry-based channel model including the arbitrary trajectory of unmanned aerial vehicle (UAV), the power radiation patterns of intelligent reflecting surface (IRS) reflecting elements and transmit antenna elements, mutual coupling among IRS row and column reflecting elements, and IRS coverage area is proposed in this article. In the line-of-sight (LoS) dominated communication scenarios, only part of the signal power can be reflected by IRS, and the performance gain of the UAV-enabled systems can be enhanced by using the reflected signal power. The mutual coupling among IRS reflecting elements, which limits the performance gain of IRS-assisted systems, is also investigated in the proposed model. Due to the limitation of coverage area of IRS, the IRS is not always effective in the process of UAV movement, and the activated conditions of IRS are also derived. In order to fully consider the influence of UAV's trajectory, we investigate the time-varying parameters including azimuth angles, elevation angles, and suboptimal reflection phases of IRS when it is activated. In the proposed model, we also investigate the influence of the mutual coupling among IRS reflecting elements on spatial-temporal correlation and ergodic channel capacity. Numerical results reveal that the mutual coupling of IRS reflecting elements reduces the performance gain of IRS-assisted systems. Also, it can be observed that IRS coverage area affects the performance gain of IRS-assisted systems, and when both UAV and receiver (Rx) are in IRS coverage area, the performance gain can be enhanced.