Study On Distribution Optimization And Load Balancing For HAPS In The Near Space

The near space refers to the ground at a distance of 20-100 km from the near earth space.As the interconnection communication carrier of the information acquisition and distribution network,the space crafts have many advantages including wide coverage,flexible deployment and low cost which is applied in the national defense,communications relay,emergency communications and other fields broadly.Compared with the ground base stations,the High Altitude Platform Stations(HAPS)is a new communication infrastructure in the near space network.Its coverage radius is large,the system capacity is high,and it can provide broadband and high speed data service transmission.In the near space emergency communication scenario,in order to ensure the seamless coverage,the coverage range of HAPS will be overlapped with each other to some extent,which leads to the difference of user's signal-to-noise ratio computation and power allocation.Consequently,the near space communication scenario is different from traditional non overlapping node planning.Usually emergency communication is accompanied with large-scale,long-range migration and users' aggregation,also the distribution of traffic varies with time and space.When the distribution of the whole user is the same,while the local users are migrating and aggregating at a certain time period,it is easy to cause the overload of the cooperative nodes.How to covers a given area effectively,allocates resources dynamically and meets the time-varying reliable communication needs is vital to the HAPS optimization.That is to determine the optimal number and location of the HAPS and to achieve the dynamic adjustment methods for the load balancing of all the HAPS.Therefore,combining with the project "Analysis and Optimization on Network Capacity of Near Space Communication Network with Dynamic Topology",this thesis focuses on the layout optimization and load balancing of near space platform.(1)The traditional base station planning belongs to the classic hexagonal cell category,but the coverage of the HAPS is large enough to ensure user coverage.Every cell edge overlaps inevitably,not the same as the traditional rule hexagonal cell.Although orthogonal frequency division multiplexing technology transmission scheme can greatly reduce the co-channel interference in the cell as a special multiple carrier,but the inter cell interference still exists.Through sharing channel information and user data information from multiple base stations which are servicing the same users at the same time,coordinated multiple point(CoMP)joint transmission and receiving technology turns the inter cell interference signal into useful signal.Therefore,considering of the green communication and the cost of base station erection,we determine two objective functions which are the lowest total power consumption and the minimum number of the HAPS.According to the objective functions,aiming at the large radius of overlapping coverage,this thesis establishes a mathematical HAPS optimization model and uses the nested algorithm to solve the model.The numerical simulation results were analyzed that can provide reference to the base stations planning with a large radius overlapping in near space communication network.(2)The optimized HAPS can provide users with less total power consumption and the number of stations.But when the overall user distribution is unchanged,and the local area has large scale migration or aggregation phenomenon at a certain time,it is easy to cause the overload of the collaborative nodes in the area.At present,the research methods of load balancing for base stations are mainly based on resource allocation,user switching and cell coverage extension.However,load balancing still needs to solve user interference problems.Aiming at overlapping scenarios,this thesis proposes a load balancing algorithm based on low load cooperative clusters which not only achieves the load balancing of the HAPS,but also overcomes the performance degradation of the edge users due to interference.In order to guarantee the quality of user communication,this thesis evaluates the traffic volume of HAPS and the call blocking rate of the users in multiple point cooperative load balancing.