Research On Resource Allocation Algorithms In Symbiotic Communication Systems For Future Internet Of Things

With the digital transformation and intelligent upgrade of modern society,the Internet of Things(IoT)has emerged as a vital component of the new national infrastructure and has been extensively applied in fields such as smart cities,intelligent transportation,and the industrial internet.Supporting large-scale IoT communications with limited spectrum and energy resources has become a critical challenge facing modern wireless communication.Symbiotic communication is an innovative communication technology that integrates active communication with backscatter communication.In this system,backscatter devices(BDs)utilize the radio frequency signals from the active communication system for backscatter transmission,eliminating the need to generate their own RF signals and thereby significantly reducing power consumption.Moreover,as both systems share the same spectrum resources,spectrum efficiency is greatly enhanced.By leveraging widely deployed cellular networks as active communication systems,symbiotic communication is envisioned to facilitate massive IoT communications with low power consumption and high spectrum efficiency.However,with the massive device connectivity demands of future IoT,designing access schemes for multiple backscatter devices within symbiotic communication systems,and appropriately configuring cellular base station(BS)beams,power,and other system resources to meet the performance requirements of both IoT and cellular transmissions remains a pressing challenge.Additionally,since the backscatter link signal is quite weak due to the double fading effect,it is challenging for backscatter devices to support multiple IoT transmissions simultaneously,making the enhancement of backscatter device transmission capabilities another urgent issue to address.To address the above critical challenges,this dissertation is dedicated to the research on resource allocation algorithms in symbiotic communication systems by exploring the access schemes for backscatter devices and enhancing their information transmission capabilities with the reconfigurable intelligent surface(RIS).This dissertation is mainly composed of four research contents,including(1)Access schemes for multiple backscatter devices in symbiotic communication systems?(2)Beamforming optimization schemes for cellular base stations in symbiotic communication systems?(3)Joint beamforming design and optimization for passive RIS-enabled symbiotic communication systems?(4)Joint beamforming design and optimization for active RIS-enabled symbiotic communication systems.The specific research works are summarized as follows:Firstly,this dissertation investigates access schemes for multiple backscatter devices in symbiotic communication systems.Specifically,in scenarios where multiple backscatter devices surround a cellular user,the simultaneous access(SA)and selective diversity access(SDA)schemes have been proposed,and the closed-form expressions of ergodic rates and outage probabilities for cellular and backscatter transmissions have been derived.The relationship between ergodic rates and the number of backscatter devices has been studied,which reveals the optimal access scheme with different numbers of backscatter devices.The simulation results have been provided to verify theoretical analysis and compare the proposed access schemes.When the number of backscatter devices is large,the SA scheme is preferable since it guarantees a significantly better rate performance.When the number of backscatter devices is small,the SDA scheme is more appealing since it can significantly reduce the computational complexity while achieving more than 85% of the rate performance of the SA scheme.Secondly,this dissertation explores beamforming optimization schemes for cellular base stations in symbiotic communication systems.Specifically,for a multiuser multipleinput and single-output(MISO)symbiotic wireless system,this dissertation proposes to treat the reflective links from the backscatter devices as a multipath component of the cellular link and considers the channel uncertainties caused by IoT information transmission and their impact on cellular transmissions.Under the cellular transmission outage probability constraints and backscatter transmission sum rate constraints,the transmit power is minimized by designing the beamforming vectors at the base station.The beamforming optimization algorithm based on semi-definite programming(SDP),and difference-ofconvex(DC)techniques is proposed to solve the formulated power minimization problem.Further,for scenarios where backscatter devices transmit information to nearby cellular users based on proximity access principles,a direction of arrival(Do A)-based beamforming optimization scheme has been proposed,which utilizes the Do As and angular spreads(ASs)of the cellular links to design the beamforming vectors,thus avoiding the prohibitive channel feedback.The simulation results have shown that the Do A-based beamforming optimization scheme achieves comparable performance as the channel state information(CSI)-based optimization scheme when the ASs are small.Thirdly,to enhance the information transmission capability of backscatter devices,this dissertation studies the joint beamforming design and optimization for passive RISenabled systems.A passive RIS consists of multiple passive reflective elements.This dissertation proposes to use passive RIS as a backscatter device to enhance the backscatter link and enable multiple IoT information transmissions.Two transmission schemes have been proposed,namely,the space-division and time-division schemes.In the former,the passive RIS simultaneously transmits multiple IoT information streams to multiple IoT receivers,while in the latter,it transmits a single IoT information stream to the corresponding receiver at a time.Joint beamforming design schemes for the BS and RIS have been proposed to minimize total power consumption while considering cellular and IoT transmission rates and passive RIS amplitude constraints.The original problem is divided into two optimization sub-problems: one is to optimize the transmit beamforming at the BS while the other is to optimize the phase shift matrix at the passive RIS.The sub-problems are solved iteratively by using the alternating optimization(AO)algorithm.Simulation results show significant reductions in power consumption supporting multiple IoT transmissions with a sufficient number of reflective elements.Finally,building on the preceding research,this dissertation replaces the passive RIS with an active RIS to further enhance the information transmission capabilities of backscatter devices and investigates the joint beamforming design and optimization in such a system.Unlike passive RISs,which can only reflect signals passively,active RISs can amplify the incident signal while adjusting phases,which strengthens the reflective link and further enhances the capability to transmit multiple IoT information streams.However,active RIS inevitably amplifies noise signals as well and requires additional power consumption.This dissertation proposes space-division and time-division transmission schemes,and minimizes the system’s total power consumption through the joint optimization of the BS’s transmit beamforming and the active RIS’s reflection coefficient matrix,under the cellular and IoT transmission rates and the active RIS’s reflection coefficients constraints.An AO algorithm based on SDP and successive convex approximation(SCA)is presented to solve the joint beamforming optimization problem in both schemes.Simulation results indicate that the introduction of active RIS can further reduce the system’s power consumption when the IoT transmission rate requirement is high.