A time-varying transition channel model for air-ground communication

In traditional wired or cellular communication, the communication scenario and channel are fixed. However, with an increasing interest in air-ground integrated communication network, communication scenario transition caused by dynamic and high-movement nodes happens frequently, resulting in deteriorating reliability of communication. In this paper, a time-varying channel model is proposed to describe the continuous-time characteristics of scenario transferring process. The model constructs the geometric structure firstly. According to the structure, the characteristic of line-of-sight (LOS) and ground-reflection propagation path are analyzed in scenario transferring process, and the velocity and position of ground nodes are formulated as function of continuous-time. Moreover, the value of parameters of transition model is proposed with scenario changing referred to stochastic tap-delay-line (TDL) model and measured data. Simulation shows that the proposed model could effectively describe the continuous transition of channel when scenario is changing. In addition, considering the requirements of low-altitude air-ground channel measurement, a special channel sounder system based on universal software radio platform (USRP) is designed, which has small size and weight, and could be carried for drone or high-altitude platform (HAP). Test result shows that the channel sounder system could measure time delay, multipath power and Doppler frequency, and the response for Doppler frequency could be modeling as a linear function.