Research On High-Reliability Data Transmission Method In Wireless Body Area Network

Wireless Body Area Network(WBAN),which has widely application prospects in telemedicine,security monitoring,entertainment and so on,has been highly valued by many scientific research institutions and high-tech enterprises.The WBAN is deployed around the human body,whose application is also closely related to the human body.So how to improve the reliability of the transmission process has become an important issue.A number of existing methods can not be applied well because WBAN has many differences with the traditional wireless sensor network in terms of energy resources,mobility,channel characteristics,data types and so on.Currently,owing to lack of the research about this issue,it is urgent and important to study the method of reliable transmission in wireless network.The main factors that lead to the decline of the reliability of WBAN are as follows: 1)the nodes on the shared channel are in conflict with each other;2)they are seriously disturbed by the neighboring network;3)the wireless link condition is extremely unstable with the human activity.To resolve the problems,on the basis of relevant research and the full consideration of WBAN channel characteristics,this thesis uses channel access mechanism,interference mitigation mechanism and relay node decision mechanism as entry points.Three methods for making data transmission reliable in WBAN are proposed.The simulation experiments and comparisons are carried out.The main works of this thesis are listed as follows:Firstly,for intra-WBAN,the contention window size of traditional backoff algorithm often fluctuates violently.Therefore,this thesis adopts Fibonacci Sequence Backoff algorithm with priority considered in unsaturated state.The performance of this algorithm is analyzed by the Markov chain model of backoff state,and it is compared with the Alternative Binary Exponential Backoff algorithm of IEEE802.15.6 standard.The simulation results showed that the proposed method can raise the normalized throughput,reduce the average frame service delay as well as packet average energy consumption,and avoid the transmission failure caused by the collisions in both homogeneous and heterogeneous conditions.So that data with different priorities can be transmitted reliably.Secondly,for inter-WBAN,there is a serious problem of the interference for WBANs in their aggregation area.A reservation based on channel access control method is put forward to alleviate interference.It utilizes the neighbor list established by beacon and appropriate channel switching mechanism to reschedule transmission.The channel idle detection is added to avoid collision in case of the neighbor list is incomplete.This thesis gives the analysis of the maximum number of WBANs that can be supported,rescheduling delay,throughput,etc.Simulation results show that when compared with the IEEE 802.15.4 beacon-enabled mode and a Time Division Multiple Access(TDMA)scheduling scheme with beacon back-off procedure,it can well improve the performance of conflict probability,throughput and power consumption,it can also effectively mitigate the interference of neighbor WBANs on data transmission reliability.Finally,besides the above research based on the single hop star topology,when the channel link loses seriously and using the extended two hop star topology in IEEE 802.15.6,the optimal relay selection problem must be solved.This thesis presents a relay node selection method based on Analytic Hierarchy Process(AHP).First,candidate relay table is constructed through candidate relay discovery phase.Then the hierarchical model with the goal of high reliable transmission is constructed,whose middle layer consists of decision factors.Using the reciprocal matrix,the candidate with maximal global weight will be selected as the best relay node by feature vector method.Considering the direct link between the node and the coordinator may recovery again,this method further adds the direct connection recovery phase.There four different application scenarios for simulation.When compared with the IEEE802.15.6 protocol,the proposed method can decrease both latency time and energy consumption greatly,and guarantee higher than 90% of the packet acceptance rate for all scenarios until the link loss ratio is less than 60%.This method makes the transmission reliable when the link is not stable.To sum up,the methods proposed in this thesis are in accordance with the characteristics and requirements of WBAN and can improve the reliability of transmission.