| The increasing ageing of the world's population,the continuing rise in the prevalence and mortality rates of various chronic diseases make the provision of quality,affordable and sustainable healthcare services the greatest challenge facing society today.Therefore,driven by the rapid development of new generation wireless communication technology,the continuous progress of medical technology and the increasing demand of public health,the human-centric,data-driven,communicationmediated,and demand-driven Wireless Body Area Networks(WBANs)have received extensive attention from all fields in the world.WBAN is a short-range wireless selforganized network consisting of several sensor nodes with different functions placed on different parts of the human body(e.g.,outside,on the body surface or inside)and access points for portable mobile devices.WBANs can effectively accelerate the indepth integration of traditional medical applications and new technologies,realize real-time monitoring of vital signs and emergency medical treatment,and establish a personal intelligent medical system of universal health information.Different from traditional wireless sensor networks(WSNs),the energy supply,computing capability,storage capacity and communication distance of each sensor node in WBANs are not only limited,but WBANs are also highly dynamic network that change with its network topology or human movement posture,which inevitably affect the channel state information(CSI)in an unpredictable way.The traditional WBANs focus on the time delay and information transmission throughput,which does not characterize the system's communication performance from the perspective of information value,nor does it meet the needs of real-time network status update.Therefore,it is of great research significance and application value to establish an energy-efficient,highly reliable and real-time energy harvesting and information transmission mechanism in WBANs.However,no description of energy harvesting and information transmission techniques that meet the needs of multiple scenarios has been found,and there is a lack of effective methods for quantifying the uncertainty of CSI and the metrics for real-time information transmission.To address the problems of limited energy harvesting environment,the channel estimation error uncertainty and the difficulty in measuring real-time information transmission in WBANs,this paper develops an in-depth study on the information uncertainty and freshness of WBANs based on energy harvesting from three dimensions: Network Architecture-Channel Reliability-Communication Performance,constructs energy harvesting and information transmission models for WBANs under different scenarios,proposes a distributionally robust optimization(DRO)algorithm under the CSI uncertainty,and verifies the feasibility of information freshness as a communication performance evaluation standard in WBANs.The main contents and contributions are as follows.(1)To address the energy limitation problem of sensors due to its size and application environment in traditional WBANs,this paper presents a study on energy harvesting and information transmission in different scenarios,and constructs an efficient hybrid structure energy harvesting and information transmission model for multiple scenarios.In this paper,the research is based on the following three aspects:1)in terms of control strategies for energy harvesting and information transmission in WBANs,a transmission power optimization algorithm based on the control time ratio is proposed;2)in terms of energy harvesting and information transmission in WBANs under normal conditions,a power optimization algorithm based on the power allocation structure is proposed;3)in terms of energy harvesting and information transmission in WBANs under abnormal conditions,a transmission power optimization algorithm based on the time allocation structure is proposed.The simulation results show that the adaptive allocation of sensor transmission power is achieved in different application scenarios of energy harvesting and information transmission,which effectively optimizes the system information throughput and greatly improves the system communication performance,providing new ideas for future research on energy harvesting and information transmission in WBANs.(2)To address the problem of the CSI uncertainty in WBANs,this paper presents a study of uncertain information based on energy harvesting,and establishes a distributionally robust information transmission mechanism applicable to different scenarios.This paper proposes a backscatter communication-assisted computational task offloading to enhance the communication and computational capabilities of the network.A DRO model based on data transmission chance constraint and energy harvesting chance constraint is established for the uncertainty of CSI in WBANs.It is assumed that the channel estimation error of static scenarios follows a Gaussian distribution,and the channel estimation error of abnormal dynamic scenarios follows an arbitrary distribution.The Bernstein Type Inequality(BTI)method and Conditional Value-at-Risk(CVa R)method are used to transform the uncertain set of the chance constraints into a semi-positive definite program for different channel distributions,respectively.A low-complexity DRO iterative algorithm is proposed for solving nonconvex optimization problems with locally solutions.Simulation numerical results compare the performance of the DRO algorithm with that of the non-robust optimization algorithm in terms of time delay.In the body surface channel,the delay of the DRO algorithm is improved by 40.5% compared to the non-robust optimization algorithm.In the body channel,the proposed algorithm achieves a delay improvement of 42.6% compared to the non-robust optimization algorithm.The analysis shows that the CVa R-based DRO algorithm can effectively quantify the channel estimation error,and the BTI-based DRO algorithm is more suitable for a certain channel error distribution.(3)To meet the requirements of high reliability and low latency communication in WBANs,the paper carries out research on information freshness based on energy harvesting,and proposes a new algorithm for information transmission based on information freshness metrics theory.In order to meet the demand for real-time information update in WBANs,this paper proposes a real-time information transmission measurement theory based on the freshness of information,and reveals the age of information(Ao I)in the process of real-time information transmission.To address the problem of CSI uncertainty,a DRO model is established to minimize the upper bound of the Ao I under the energy harvesting and information transmission chance constraints,and the CVa R-based method is used to transform the distributionally robust chance constraint into a semi-positive definite program,and an algorithm is proposed for minimizing the upper bound of the Ao I based on the information freshness metric.Simulation result verifies the effectiveness and reliability of Ao I to measure the information freshness in WBANs,and reveals that there is a trade-off relationship between Ao I and energy consumption.The proposed algorithm improves the average Ao I by 22.7% compared to the non-robust optimization algorithm,which demonstrates that the algorithm can guarantee the freshness of medical information under relatively poor channel conditions. |
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