Ultra-reliable And Low-latency Wireless Transmissions And Cooperative Control

As the development of wireless communications has entered a brand new stage,it needs not only to deal with the explosive increase of future mobile data,but also to deeply integrate with vertical industries,opening a new era of Internet of everything.Some emerging applications such as intelligent trans-portation and "Industry 4.0" are gradually changing people's lives.In order to meet the rigorous requirements of latency and reliability for the emerging applications,wireless communication systems should have the abilities of sup-porting an end-to-end latency within a few milliseconds and a reliability down to 99.999%.However,the existing wireless communication systems are mainly designed from the aspect of efficiency,and cannot fully satisfy the real-time and reliable requirements.Therefore,what is needed now is to carry out the re-lated researches on ultra-reliable and low-latency communications(URLLCs).In this thesis,we focus on ultra-reliable and low-latency wireless transmis-sions and cooperative control.Our works can be divided into the following four perspectives.First of all,this thesis investigates the performance analysis methods for URLLCs,with the aim of revealing the inherent tradeoff between latency and reliability,and providing the theoretical support for the subsequent chapters.Then,taking vehicle-to-infrastructure(V2I)communications as the research scenario,this thesis studies the twin-timescale radio resource man-agement aiming to meet the URLLC requirements.Thirdly,taking vehicle-to-vehicle(V2V)communications as the research scenario,this thesis investigates the joint frame design and resource allocation,in order to reduce the impacts of overhead on the extremely short frame.Finally,this thesis jointly optimizes the control efficiency and energy consumption for Internet of things(IoT)control systems operating with URLLCs,aiming to let communications better "serve"control more energy-efficiently.The main contents of this thesis are summarized as follows.(1)Performance Analysis Methods for Ultra-Reliable and Low-Latency CommunicationsTo reveal the inherent tradeoff between latency and reliability,this thesis studies the performance analysis methods for URLLCs from multiple perspec-tives.Specifically,various types of latency and reliability that may exist in communication networks are first sorted and summarized.Then,the trans-mission latency and reliability are studied from the perspective of the physi-cal layer,including the classical modeling,large-packet transmission modeling and short-packet transmission modeling.In addition,this thesis investigates the queuing latency and reliability from the perspective of the media access control(MAC)layer,including the Little-based modeling and violation probability-based modeling.Finally,we discuss and explain the latency and reliability studied in the subsequent chapters.(2)Twin-Timescale Radio Resource Management for Ultra-Reliable and Low-Latency CommunicationsConsidering highways in vehicular networks,this part studies the twin-timescale radio resource management for URLLCs.Due to the high mobility of vehicular networks,it is not practical to acquire instantaneous channel state information(CSI)and make radio resource allocation based on such short-term CSI,while meeting the URLLC requirements.In this thesis,considering the downlink of a V2I system conceived for URLLCs,we optimize the perfor-mance of transmission latency based on idealized perfect and realistic imper-fect CSI.Compared to the time-scale of CSI fluctuation on the millisecond level,those of vehicle density and location fluctuations are higher.In order to avoid the frequent exchange of instantaneous CSI,a two-stage radio resource allocation problem is first formulated based on a novel twin-timescale perspec-tive.Specifically,based on the prevalent vehicle density,Stage 1 is constructed for minimizing the worst-case transmission latency on a long-term timescale.In Stage 2,the base station allocates the total power at a short-term timescale according to the large-scale fading CSI encountered for minimizing the maxi-mum transmission latency across all vehicular users.Then,a primary algorithm and a secondary algorithm are conceived for our V2I URLLC system to find the optimal solution to the twin-timescale resource allocation problem,with spe-cial emphasis on the imposed complexity.Finally,our simulation results show that the proposed resource allocation scheme significantly reduces the maxi-mum transmission latency,and it is not sensitive to the fluctuation of vehicle density.(3)Joint Frame Design and Resource Allocation for Ultra-Reliable and Low-Latency CommunicationsConsidering urban intersections in vehicular networks,this part studies the joint frame design and resource allocation for URLLCs.Vehicular commu-nications mainly focus on the exchange of driving safety information,which requires the support of URLLCs.However,the frame size is significantly shortened in URLLCs because of the rigorous latency requirements,and thus the overhead is no longer negligible compared with the payload information from the perspective of size.In this thesis,we investigate the frame design and resource allocation for an urban V2V URLLC system in which the uplink cel-lular resources are reused at the underlay mode.Specifically,we first analyze the lower bounds of performance for V2V pairs and cellular users based on the regular pilot scheme and superimposed pilot scheme,including the tradeoff among spectral efficiency,transmission latency and reliability of V2V pairs,as well as the signal-to-interference-plus-noise ratio of cellular users.Then,based on the lower bounds,we propose a frame design algorithm and a semi-persistent scheduling algorithm to obtain the optimal frame design and resource allocation with the reasonable complexity.Finally,our simulation results show that the proposed frame design and resource allocation scheme can greatly sat-isfy the URLLC requirements of V2V pairs and guarantee the communication quality of cellular users.(4)Leveraging Linear Quadratic Regulator Cost and Energy Con-sumption for Ultra-Reliable and Low-Latency IoT Control SystemsCurrently,the design of control,sensing and communications is isolated at present in IoT.In this thesis,we investigate the joint optimization of con-trol cost and energy consumption for a centralized wireless networked control system.Specifically,with the "sensing-then-control" protocol,we first develop an optimization framework which jointly takes control,sensing and commu-nications into account.In this framework,we derive the spectral efficiency,linear quadratic regulator cost and energy consumption.Then,a novel perfor-mance metric called the energy-to-control efficiency is proposed for the IoT control system.In addition,we optimize the energy-to-control efficiency while guaranteeing the requirements of URLLCs,thereupon a general and complex max-min joint optimization problem is formulated for the IoT control system.To optimally solve the formulated problem by reasonable complexity,we pro-pose two radio resource allocation algorithms.Finally,simulation results show that our proposed algorithms can significantly improve the energy-to-control efficiency for the IoT control system with URLLCs.