| With the aggravating trend of aging population and the increasing treat of chronic disease to human body,mobile-health(m-health)has already become one of the most effective methods to release the requiring burden of medical resource and cut down the increasing cost of medical care.Wherein,Wireless Body Area Networks(WBANs)play an important role in the development procedure of m-health.However,as the transporter of important medical information,WBANs have to satisfy the strict requirements for wireless communications.As an important part in WBAN's protocol stack,Media Access Control(MAC)layer is of great important that severely influences the communication performance of WBANs.Taking WBANs as research scenario and referring to reliability,energy-efficiency and throughput as performance metrics,this dissertation firstly investigates the relay mechanism in WBANs that is compatible with IEEE 802.15.6 standard and improves the network lifetime.Then the power control methods which utilize MAC frame transactions to calculate optimal transmission power is studied.Thirdly,considering the possible multi-WBANs scenarios in medical applications,the dissertation designs an individual distinguished coexisting mechanism to deal with the coexisting problem.The main contributions of the dissertation are listed as follows:1.In the second chapter,a relay mechanism in MAC layer of WBANs is proposed that is compatible with IEEE 802.15.6 standard and improves the network lifetime.The proposed mechanism contains relay selection algorithm and relay selection update methods,which prolongs the network lifetime of WBANs to the most extent through equalizing the energy consumption among sensor nodes.Specifically,considering both energy consumption rate and energy storage of sensor nodes,we firstly formulate an optimization with the target of maximize the lifetime of sensor node that has the minimum lifetime in the network under the topology restriction specified in IEEE 802.15.6 standard.To acquire optimal relay selection scheme,we design a heuristic algorithm(LMRSS)to rapidly solve this optimization.Secondly,two relay update methods are designed to deal with relay update of WBANs.Then,a relay mechanism is designed and its compatibility with IEEE 802.15.6 standard is discussed.Finally,through the simulation results,we prove the low time complexity,convergency and effectiveness of LMRSS,discuss the important parameter adjustments in two update methods.Comparing with existing relay mechanism,our proposed relay mechanism can prolong more than 10% network lifetime of WBANs.2.In the third chapter,a relay-aided transmission power control method is proposed to address the problems that appear in the implementation of existing power control methods on WBAN scenarios.The proposed method effectively combines transmission strategy selection and transmission power calculation together to overcome the existing problems in power control implementation and conserve the energy of relay node with the guarantee of transmission reliability.Specifically,we firstly conduct experiments to indicate the possible problems appear in power control method of WBANs,which are long distance problem and energy crisis of relay node,and discuss the possible methods to solve these two problems.Then,according to the experiment results and the discussion,two transmission strategy selection methods are proposed to deal with the scenarios that consider energy harvesting and the scenarios that don't take energy harvesting into account,respectively.Based on the transmission strategy selection results,transmission power of sensor nodes can be accurately calculated according to the prediction of wireless channel conditions.Integrating the strategy selection methods and power control calculations together,two relay-aided transmission power control methods are designed for energy harvesting scenarios and non-energy harvesting scenarios,that is RA-TPC and EHRA-TPC,respectively.The proposed method utilizes direct transmission to save the energy of relay node when the channel condition is good,while switches to relay-aided transmission to guarantee reliability when channel condition is bad.And then,base on transmission strategy selection,the corresponding transmission power is calculated.Herein,EHRA-TPC utilizes fuzzy logical system to fulfil transmission strategy selection.In addition,two important tunable parameters in RA-TPC are discussed for different application scenarios.Finally,the simulation results demonstrate that our proposed power control methods can effectively address long distance problem,reduce 30%energy cost of relay node with the guarantee of transmission reliability and prolong more than 40% network lifetime of WBAN in the scenarios without energy harvesting.When it comes to the scenarios with energy harvesting,our proposed method can effectively improve at most 50% coverage rate of sensor nodes in WBANs.3.Considering the possible multi-WBANs scenarios that appears in medical applications,an individual distinguished coexisting mechanism which is distributed and integrated is proposed in the fourth chapter.The proposed coexisting mechanism coordinates the transmission of coexisting WBANs with the guarantee of communication performance in the way of resource allocation and scheduling,multi-channel technology and power control.Specifically,we firstly formulate the shared timeslot allocation model in game theory and then prove the existence and uniqueness of nash equilibrium in this game.Next,in order to obtain the unique nash equilibrium,a distributed timeslot allocation algorithm is designed which is mathematically proven to be effective and convergent.Secondly,taking this timeslot allocation algorithm as the core,an individual distinguished integrated coexisting mechanism is proposed,which consists of access control module,timeslot allocation module,active period scheduling module and power control module.Specifically,Access control and Active period scheduling are designed referring to the coexisting methods specified in IEEE 802.15.6standard.Also,power control utilizes mobility prediction to adjust transmitting power for each coexisting WBAN.Finally,The simulation results demonstrate that the proposed mechanism is stable and convergent and can realize differentiated time slot allocation depending on WBANs' requirement conditions.Furthermore,based on medical care scenarios,the simulation results show that,when compared with coexisting mechanism specified in IEEE802.15.6,our coexisting mechanism can improve at most 16% transmission reliability and25% network throughput with a high level energy efficiency performance. |
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