Research On Efficient Ray-tracing Algorithms For Next Generation Wireless Communication

The conventional ray-tracing technology is facing new opportunities and challenges because of the need for higher accuracy and higher efficiency in channel modelling in the upcoming generation of wireless communication system,and the need to make the modelling approaches more suitable for the new millimetre-wave and large-scale antenna system.Based on the original ray-tracing channel simulation platform in the laboratory,this thesis continuously optimizes it and conducts a thorough study from electromagnetic environment modelling and transceiver module,and summarizes the improvement of ray-tracing technology and proposes corresponding solutions:A method to select the electromagnetic parameters for ray-tracing channel simulation has been proposed in this thesis,which addresses the challenging practical issue in ray-tracing channel simulation,namely,how to accurately determinate the environmental electromagnetic parameters.In the proposed method,a local radio environment map is firstly constructed with the measured radio propagation data in a small part of the whole simulation area.Then,based on the perceptual hash algorithm,the measured radio environment map is quickly compared against the ray-tracing simulated radio environment map.By adjusting the electromagnetic parameters in the simulation environment,the simulated results get close to the measurement results.For reflective surfaces composed of multiple types of materials,a rasterization method is further proposed to improve the accuracy of channel prediction.The proposed method has been employed to obtain environmental electromagnetic parameters and perform ray-tracing simulation verification.Laboratory test results show that the root mean square error of the received power is 2.7 d B when using the proposed method,which is smaller than that when using the traditional method with electromagnetic parameters querying from the material library.This method can be employed to avoid field measurement(especially for those hard-reaching environment),and can also be used to update(or supplement)the electromagnetic parameters queried from the material library.To address the “ray leakage” or “ray overlapping” problem frequently encountered in the traditional SBR(shooting and bouncing ray-tracing)-based channel simulation with inaccurate receiving radius,a scenario cognition-based improving method is proposed in this thesis.In this method,the artificial neural network is employed to dynamically adjust the receiving radius,thereby improving the channel simulation accuracy of the ray-tracing algorithm.The performance of the improved SBR channel simulation algorithm is compared with the traditional SBR algorithm and lab measurement.For a single transmitting/receiving antenna,the root mean square error(RMSE: Root Mean Squared Error)of path loss obtained by the proposed method is2.6d B,which is smaller than that when using the traditional SBR channel simulation algorithm.The acceleration scheme in ray-tracing is studied in this thesis: to reduce the SBR simulation time for massive multiple-input multiple-output(MIMO)scenarios,a beam pattern-based ray launching method is proposed to improve the channel simulation efficiency when using MIMO antennas.For the simulation of 2×2,4×4,8×8 uniform distribution patch antenna array,the average time of a single simulation of received power using this method is 97% less than that of traditional SBR ray-tracing simulation.A systematic simulation acceleration scheme for channel nonreciprocity compensation is also be proposed in the thesis: after the compensation algorithm is used to correct the influence of frequency offset,the uplink channel can be directly used to estimate the downlink channel when the base station side antenna transmission angle is approximately the same as the arrival angle,the RMSE of the power delay spectrum obtained by the simulation is less than 2d B.Finally,in order to verify the effectiveness and practicability of the improved ray-tracing platform in this thesis,the channel characteristics of the asymmetric millimeter wave large-scale MIMO system were simulated and analyzed,various factors affecting the channel asymmetry were summarized.The asymmetry factor is defined to evaluate the degree of channel asymmetry.The simulation shows that the configuration of the transceiver antenna and the radio propagation environment are the main factors that affect the channel asymmetry.