Research On Efficient Utilization And Optimization Methods Of Spectrum Resources In Wireless Communication Networks

Spectrum is an important carrier of wireless communication networks,and wireless communication networks without available spectrums will only be-come empty talk.With the explosive growth of networked devices globally,tens of billions of net-worked devices will give birth to more wireless services,and thus there is an urgent need for sufficient spectrum resources to meet the massive demand of wireless spectrum access.Judging from the current situa-tion,on the one hand,the shortage of spectrum resources compels the academic and industrial circles to urgently develop higher frequency bands,which takes massive manpower and material resources;on the other hand,federal commu-nications commission(FCC)and many countries and organizations have inves-tigated and pointed out that most of the allocated spectrum has not been fully utilized,and the utilization rate is even as low as 15.2%.Therefore,reusing existing idle spectrum resources through cognition is of great significance to the alleviation of the tension of spectrum resources.With efficient utilization and optimization of wireless network spectrum resources being the mainline in this paper,the research branches out from ground wireless communication networks to hovering unmanned aerial vehicle(UAV)networks,and then it will be further expanded to the networks of UAVs moving in air.It fits the wireless communication industry,and the development trend is in line with the academ-ic research trend of wireless communication networks expanding from ground to air.The specific research content consists of the following three aspects:(1)Study of the efficient utilization and optimization of spectrum re-sources based on the wireless powered communication network(WPCN).First-ly,for the spectrum-based opportunistic wireless powered communication net-work,a three-slot structure model of "joint spectrum sensing,energy har-vesting and Non-orthogonal multiple access(NOMA)data transmission" is established.Furthermore,in the case of fixed sensing duration,a closed-form expression of the data transmission duration of the secondary user is derived,and based on this,a parameter joint optimization algorithm based on the golden section search method is proposed to maximize system uplink rate.In addition,for a wireless powered communication network based on spectrum coopera-tion,the cognitive base station simultaneously receives uplink transmission da-ta from the secondary and primary users.A three-slot structure model of "joint energy harvesting,NOMA data transmission and forwarding data of the main user”is established.In this model,with the goals of maximizing uplink data from the secondary user,the closed-form expressions of the energy harvesting time,data transmission time,and data transfer time of the primary user are de-rived.The simulation results confirmed that by introducing cognitive radio and NOMA technology to adjust and optimize the time slot structure of the wireless powered communication network,the proposed algorithm can more efficiently utilize idle spectrum resources and significantly improve the sum-rate of the wireless powered communication network.(2)Research of the efficient utilization and optimization of spectrum re-sources based on the three-dimensional hovering UAV network.With an em-phasis on the hovering UAV network,a joint optimization algorithm for the sensing duration and the three-dimensional position of the UAV is proposed to maximize the effective throughput of the hovering UAV network.Specif-ically,for a single-pair UAV communication system,a temporal-spatial two-dimensional spectrum cognition model is established.In this model,it is theo-retically proved that the optimal position of performing the sensing and receiv-ing tasks of the leading unmanned aerial vehicle(LUAV)is on the straight line between the primary user and the following unmanned aerial vehicle(FUAV)performing the uplink data task,which greatly simplifies the constraint of the feasible area of deployment of LUAV,and a joint optimization algorithm based on the alternate iteration of the sensing duration and the three-dimensional po-sition of the UAV is proposed to maximize the system's effective throughput.Then,for the multi-FUAV communication system,a multi-UAV transmission model based on time division multiplexing is established,and the "divide and conquer”strategy and the“weighted sum”method are adopted to propose an approximate optimal algorithm based on throughput weighting.In addi-tion,in order to reduce the complexity of the throughput weighting algorith-m,a closed-form expression for the optimal three-dimensional position of the UAV is derived,and a low-complexity approximate optimal algorithm based on the weighted sum of positions is proposed.The simulation results show that the proposed alternative iterative algorithm has the advantage of fast conver-gence,and confirms that the proposed algorithm has almost no loss in system performance compared with exhaustive search optimization algorithm while greatly reducing the complexity of the algorithm.The system performance,compared with fixed LUAV location strategy and the single-time dimension spectrum sensing strategy,has been significantly improved.(3)Research on efficient utilization and optimization of spectrum re-sources based on moving UAV network.Aiming at the moving UAV network,a joint optimization algorithm for UAV trajectory and spectrum access is pro-posed,and the spectrum efficiency and energy efficiency of the system are an-alyzed separately.Specifically,first,considering the impact of UAV trajectory on spectrum sensing and data transmission,the minimum step distance con-straint of UAV to the destination for each time slot is established,and a joint optimization algorithm based on alternate iterations is proposed to optimize the parameters such as UAV trajectory,transmission power and spectrum sensing duration.The data transmission rate of the system is maximized under anti-collision constraints,flight speed constraints and the UAV network's interfer-ence constraints to the primary user on the ground.Second,further considering the influence of UAV trajectory on parameters such as spectrum sensing,da-ta transmission and UAV energy consumption,joint optimization algorithm of FUAV trajectory,transmission power and spectrum sensing duration to max-imize the energy efficiency are redesigned.The simulation results show that the proposed algorithm for UAV trajectory,transmission power and spectrum sensing time joint optimization has the advantage of rapid convergence,and also confirms that the proposed algorithm,compared with UAV fixed straight flight strategy and single-time dimension optimization strategy system,has a significantly improved performance.