【作者】 杨涛；

【导师】 焦健；

【作者基本信息】 哈尔滨工业大学 ， 电子与通信工程（专业学位）， 2021， 硕士

【摘要】 卫星物联网(Satellite-based Internet of Things,S-Io T)能实现全球覆盖,提供随时随地接入的能力,已经成为下一代移动通信的重要发展方向之一。但是,虽然S-Io T能够提供广域覆盖,如何保障海量Io T用户设备的高效接入仍然是一个开放难题。与此同时,卫星与地面Io T用户设备之间数百公里以上的距离会产生较大的传播时延,使得S-Io T面向大规模机器型通信(massive Machine Type Communication,m MTC)的高时效大规模接入面临更进一步的挑战。基于此,本文面向未来S-IoT广域覆盖下高时效大规模接入需求,引入了信息年龄(Age of Information,Ao I)这一时效性能指标,设计了免授权年龄优化(Grant Free Age-Optimal,GFAO)随机接入协议,通过合理增加接入时隙的数量,降低了系统的接入失败概率(Access Failure Probability,AFP),从而降低了系统的平均Ao I(Average Ao I,AAo I)并提高了系统的吞吐量。进一步,考虑S-Io T广域覆盖区域内存在多样化的时效性能需求,设计了不等时效保护(Unequal Timeliness,UT)的GFAO随机接入协议,通过将导频和时隙资源合理分配给基于不同时效优先级分组的Io T用户设备,实现了UT-GFAO随机接入方案。具体研究内容如下:面向mMTC设备的短包突发接入需求和星地链路的长传播时延特点,通过免授权机制降低了握手次数,提出了GFAO随机接入协议。激活的Io T用户设备随机选择导频进行接入,卫星可以利用接收信号功率和统计信道信息来较为准确的识别导频冲突。然后,构造了单个Io T用户设备的瞬时Ao I演进图,推导了系统AAo I的表达式,并以此推导了AAo I和系统吞吐量的关系。仿真结果表明,给定的系统负载区域内存在最优的接入时隙数量,可以在达到最低AAo I的同时,实现最大的系统吞吐量。针对S-Io T覆盖区域下多样化的业务时效需求,进一步研究了m MTC设备按时效优先级的UT-GFAO随机接入协议,通过合理分配导频资源,不同时效需求的Io T用户设备在不同的子帧能够分组高效接入。UT-GFAO随机接入协议包含两种方案,即独立分级接入(IUT)和扩展分级接入(EUT)方案。其中,IUTGFAO可以在满足不同时效优先级分组Io T用户设备的AAo I需求基础上,在各自的接入子帧上实现高时效接入。同时,EUT-GFAO基于前述推导的给定时隙数量下存在达到最低AAo I的系统负载这一结论,合理利用高优先级Io T设备组的剩余导频和时隙资源,为低优先级Io T用户设备组提供用户卸载从而缓解了导频冲突问题,降低了低优先级Io T用户设备组的AAo I。分析了不同时效优先级分组的Io T用户设备瞬时Ao I演进图,推导了两种UT方案中不同优先级组用户的AAo I。仿真验证了UT-GFAO随机接入协议可以保障多样化时效需求业务的分组高效接入。更多还原

【Abstract】 Satellite-based Internet of things(S-IoT)can realize global coverage and provide anytime and anywhere multiple access,which has become one of the important development directions of the next generation mobile communication.However,although S-Io T can provide wide area coverage,how to ensure the efficient access of massive Io T user equipment is still an open challenge.Meanwhile,the long distance between satellite and terrestrial Io T user equipment,which is more than hundreds of kilometers,will produce large propagation delay,which makes the age-optimal massive access of S-Io T for massive machine type communication(m MTC)face great challenges.On this basic situation,a timeliness performance indicator named age of information(Ao I),is introduced,and a grant free age-optimal(GFAO)random access protocol is proposed to satisfy age-optimal massive access requirements for the future wide area coverage of S-Io T.By reasonably increasing the number of access time slots,the access failure probability(AFP)of the system is reduced,which reduces the system average Ao I(AAo I)and improves the system throughput.Further,considering the diversified timeliness requirements in the wide area coverage of S-Io T,unequal timeliness(UT)is designed for GFAO random access protocol to realize the UTGFAO random access scheme,by reasonably allocating pilot and time slot resources to different timeliness priority Io T user equipment groups.The specific research contents are as follows:Facing the short packet burst access requirements of m MTC equipment and the long propagation delay characteristic of satellite-terrestrial link,the number of handshakes is reduced through the grant free mechanism,and the GFAO random access protocol is proposed,where the activated Io T user equipment randomly select the pilot to access,and the satellite can accurately identify the pilot collision by utilizing the received signal power and statistical channel information.Then,based on the instantaneous Ao I evolution of a single Io T user equipment,the expression of system AAo I is derived,and the relationship between AAo I and system throughput is also deduced.The simulation results show that under a given system load segment,there is an optimal number of access slots,which can achieve a minimum AAo I and a maximum system throughput.Aiming at the diversified timeliness requirements of services in the wide area coverage of S-Io T,the UT-GFAO random access protocol for m MTC equipment with different timeliness priority is further studied.By reasonably allocating pilot resources,Io T user equipment with different timeliness requirements can send status update packets efficiently in different subframes.UT-GFAO random access protocol includes two schemes: independent unequal timeliness(IUT)access scheme and extended unequal timeliness(EUT)access scheme,where IUT-GFAO can realize ageoptimal access of different timeliness priority Io T user equipment group on their respective access subframes,based on meeting the AAo I requirements.At the same time,based on the conclusion that under a given number of access time slots,there is a system load can achieve the lowest AAo I derived above,EUT-GFAO allows rational use of the remaining pilot and time slot resources of the high timeliness priority Io T user equipment group to provide user uploading for the low timeliness priority Io T user equipment group,to alleviate the pilot collision and reduce the AAo I of the low timeliness priority Io T user equipment group.The instantaneous Ao I evolution of Io T user equipment with different timeliness priority is analyzed,and the AAo I of different timeliness priority Io T user equipment groups for the two UT schemes are derived.Simulation results show that UT-GFAO random access protocol can ensure efficient access of services with diversified timeliness requirement.更多还原