Research On Heterogeneous Network Coverage Performance In High Altitude Platform Station

With the rapid development of wireless communication technology and the growing demand for ubiquitous communication,research on nonterrestrial networks is becoming more and more advanced.Among them,High Altitude Platform Station(HAPS),as a stratospheric communication carrier located between terrestrial and satellite networks,has great prospects for application in remote areas with wide coverage and emergency deployment.However,due to the hardware of the platform carrier and the characteristics of the stratospheric atmosphere,the random disturbances generated by the quasi-stationary HAPS in the air will have a great impact on the ground coverage effect.Therefore,this study focuses on the coverage performance of the HAPS and the heterogeneous networking scheme using ground-based IMT base stations to supplement the coverage.In the scenario where the quasi-stationary HAPS has jitter,the ground coverage performance of the aerial base station with random jitter is optimized using heterogeneous networking.After the supplementary coverage is achieved,although the link quality at the edge of HAPS cell can be improved,the random jitter of HAPS will still cause frequent handover of users located in the overlapping coverage area,and will lead to a new problem,which is the degradation of service quality caused by too many users accessing the ground station.So it is necessary to design a cell handover strategy that can effectively solve the two aforementioned problems to improve user satisfaction.As the classical hexagonal cellular coverage model and the antenna equal-beamwidth coverage model cannot accurately reflect the ground coverage effect of high altitude platforms with jitter,this thesis proposes an aerial platform ground coverage model that considers coupling loss and jitter.The core idea is that,based on the geometric principles of the classical model in the cell center arrangement and the elliptical envelope to the ground,the cell center coordinate algorithm is calibrated according to the nature of the multi-beam antenna used in HAPS,and the semi-axis of the elliptical envelope is calibrated according to the coupling loss and platform jitter,finally forming a coverage model suitable for the research scenario in this thesis.After identifying the edge areas of cells with poor ground coverage performance of HAPS,the network topology of IMT base stations with reasonable isolation distance and feasible number of supplemental coverage is designed according to the interference protection criterion between HAPS and IMT systems.After realizing the HetNet structure,for the cell handover strategy in the overlapping coverage area,this thesis designs seven attribute indicators for handover judgement based on the scenario characteristics,including the HAPS cell center drift factor,and proposes a hierarchical TOPSIS-APP multi-attribute handover decision strategy based on user location triggering.The proposed algorithm is compared with the single-level TOPSIS decision algorithm using the attributes designed in this thesis as well as the classical handover decision algorithm,and simulated in a system-level simulation platform to verify the effectiveness of the proposed algorithm in reducing the number of handover times,the number of handover failures and the handover failure rate in a HetNet under the scenario of HAPS with severe jitter.