Research On Multiple Access Techniques For Satellite-based Internet Of Things Communication Networks

As an important infrastructure of the national information network,the satellite communication network has great strategic significance in safeguarding national security and promoting economic development because of its wide coverage,geographical and climatic constraints,which are global research hotspots and the commanding heights of economic and technological competition among countries.With the fifth-generation(5G)mobile communication system coming into commercial use,the integeration of satellite communication and ground 5G has become a hot spot of concern.Among them,the Internet of Things(IoT)application is a typical application scenario in the 5G system,and its business scale is increasing year by year,which has broad application prospects.However,due to limitations of space and environment,the traditional IoT applications based on terrestrial communication systems have experienced the phenomenon of service capacity and demand mismatch in the areas of forest area,disaster monitoring,remote sea monitoring,and wildlife tracking and monitoring.The satellite communication system,by virtue of its wide coverage and strong system invulnerability,can provide access services for IoT terminals placed in remote areas,and realize the true "Internet of Everything" in a global scale.The emergence of satellite IoT systems brings new opportunities to IoT applications,but it also poses new challenges to its communication technology.How to meet the access requirements of massive users and ensure the quality of service(QoS)of users is an urgent problem to be solved since satellite multi-dimensional communication resources are limited.The multiple access technology aims to cut and allocate system resource granularity from different dimensions,and plays a vital role in improving system resource utilization,reducing terminal access delay,and saving terminal power consumption.This thesis studies the multiple access technology in the satellite IoT system.The main innovative work and achievements are as follows:First of all,aiming at the problem of designing an uplink asynchronous random access in multi-satellite cooperative communication scenarios,an asynchronous cooperative ALOHA(ACA)scheme based on space-time heterogeneous delay is proposed.The scheme takes advantage of the large number of satellite nodes in the future satellite IoT system,and adopts the idea of spatial diversity.Each data packet needs to be sent only once and can be simultaneously received by multiple satellites.At the gateway station,by exploiting the difference of the user data arrival time,the sliding correlation technology is used to determine the data packet position,and the multi-user data detection is realized by the cross-receiver iterative interference cancellation.Based on this,the author analyzes the performance of the scheme by establishing a theoretical analysis model.The results show that the ACA scheme can achieve higher system throughput without adding additional signaling and power overhead to the terminal.Secondly,for the same codebook collision resolution problem in the uplink grant-free sparse code multiple access(SCMA)process,an asynchronous flipped grant-free SCMA(AF-SCMA)scheme is proposed.By analyzing the impact of the same SCMA codebook conflict on system performance,using the idea of flipped diversity,a new data packet transmission structure is constructed,that is,each data packet and its flipped replica are encoded by different SCMA codebooks,and are sent simultaneously.At the receiver,a sliding window is used to detect multi-user data,and the iterative interference cancellation technology is used to solve the data packet conflict problem through Zigzag decoding.Based on this,the author established a theoretical analysis model to analyze the performance of the scheme,and proposed a feasible design of the preamble sequence.The results show that the proposed scheme can effectively alleviate the negative impacts of the same codebook collision in the asynchronous grant-free SCMA system,and improve the spectrum utilization within the acceptable power consumption range of the terminal.Thirdly,focusing on the problem of optimizing the distributed random access strategy of IoT terminals with energy harvesting capability in satellite IoT system,an energy harvested satellite terminal distributed random access optimal policy(EH-ST-DRAOP)is proposed.Firstly,the distributed random access strategy optimization problem is established to maximize the long-term throughput problem of the system,and the game theory is used to solve the optimization problem.Since each user adopts the same access strategy,the author proves the existence and uniqueness of the symmetric Nash equilibrium point by analyzing the satisfaction conditions of symmetric Nash equilibrium,and solves it by using the policy iterative algorithm and the bisection method.Then the author proves the obtained symmetry Nash equilibrium point is the local optimal solution to the original optimization problem.The strategy effectively manages the energy of the energy harvesing terminals in the satellite IoT system,and can achieve excellent throughput performance.Moreover,EH-ST-DRAOP can also achieve higher data transmission probability and lower access delay in a high energy harvesting rate scenario.