Researches On Channel Model Of HAP-MIMO Communication System

Because of the outstanding features of the high altitude platforms(HAPs),e.g.,large area coverage,low propagation delays,and broadcast capability,HAP communication system has been widely researched these years.Applying the multiple-input multiple-output(MIMO)technology to HAP system can improve spectrum efficiency and achieve high data rates.As an effective tool to design system,channel models can accurately describe the signal propagation characteristics and evaluate the system performance.Therefore,an accurate channel model is important for the analysis and design of HAPMIMO communication system.In this paper,the channel propagation characteristics and channel modeling methods of HAP-MIMO system are studied,and geometric based stochastic channel(GBSM)models are proposed,including a non-stationary three dimensional(3-D)channel model for wideband HAP-MIMO communication systems with relatively fast moving receivers and a 3-D HAP-MIMO channel model based on dynamic properties of scatterers.This paper develops a non-stationary 3-D channel model for wideband HAP-MIMO communication systems,where the velocity and trajectory of the receiver change with time.Wideband effects on channel impulse response are modeled by tapped delay line(TDL)structure.A non-stationary fading process is resulted by time-varying parameters including velocity and geometrical relationships among the transmitter,scatterers and the receiver.Statistical properties are studied based on a theoretical framework.In addition,the effects of velocity variations are investigated.A corresponding simulation model is developed to verify the theoretical results.Finally,numerical and simulation results show that the proposed channel model can capture the non-stationary characteristics of HAP-MIMO channel.In addition,a 3-D channel model including both stationary and moving scatterers for HAP-MIMO communication systems is proposed in this paper.Dynamic properties including the mobility and the evolution of scatterers are considered.An M-step 2-state Markov process is incorporated into this model to depict the reappearance behavior of both scatterers.The survival probabilities of scatterers are derived by using Chapman-Kolmogorov(C-K)equations,and closed-form expressions are derived in this paper.In addition,the corresponding space-time correlation function(ST-CF)is obtained,and the closed-form expression for the ST-CF of moving scatterers is derived.Finally,numerical analysis shows the ability of the proposed channel model to capture the dynamic characteristics of HAP-MIMO channel.The utility of the proposed channel model is demonstrated by comparing with measurement results.