Research On Carrier Sense Multiple Access/collision Avoidance For Wireless Body Area Network

Wireless body area network(WBAN)is a short-distance wireless communication system running in the body,surface and in vitro(from more than ten centimeters to several meters),which includes various types of sensor nodes.These nodes collect human parameters and transmit them to the coordinator,which is responsible for transmitting them to the network.WBAN emerges,with the increase of global population,the extension of human life expectancy and the gradual trend of aging.At first,WBAN was applied in the medical field to solve the shortage of medical resources and realize the sharing of medical resources,and then expanded to various fields such as daily life,entertainment,military,which has broad prospects for development.In order to promote the development of WBAN,802.15 Working Group proposed the IEEE 802.15.6 protocol in 2012.Because WBAN has large traffic and each sensor node has different traffic cycle,it widely uses Carrier Sense Multiple Access/Collision Avoidance(CSMA/CA)access method.In the research of CSMA/CA access methods,the predecessors focused on one process of CSMA/CA,but failed to accurately analyze the CSMA/CA access methods and consider its impact on the whole WBAN system from different aspects.Therefore,this paper combines the project of National Natural Science Foundation of China "Research on Green Intelligent Information Acquisition and Processing Method Oriented to Pregnant Women's Body Area Network",and studies the access method of CSMA/CA in WBAN.The specific research contents include:(1)CSMA/CA access methods are usually analyzed by markov chain model.In the process of Markov chain modeling,the value freezing process is neglected or considered only because the channel is busy.The value freezing process of the back-off counter is an indispensable part of a complete back-off counter value dropping process,which is an integral part of the whole CSMA/CA access method.Based on the detailed analysis of the value freezing process in the process of back-off counter value dropping,this paper establishes a four-dimensional Markov chain model for CSMA/CA access method,accurately analyses the whole process of CSMA/CA access method,and analyzes the model through transfer probability.(2)In IEEE 802.15.6 CSMA/CA WBAN,the non-ideal channel characteristics of WBAN are analyzed.Signal transmission in WBAN will span the human epidermis or the space range from ten centimeters to several meters along the skin surface or from the human body and will inevitably experience fading.Therefore,this paper studies the characteristics of non-ideal channel of WBAN and proposes the definition of transmission probability,collision probability,failure probability,reliability,throughput,average service delay,energy consumption and other performance indicators under non-ideal channel conditions.Through Monte Carlo experiment,the relationship among transmission probability,collision probability and failure probability as well as the influence of total number of nodes,number of retransmissions,load length and data rate on the system performance indicators are analyzed.The performance of WBAN under CSMA/CA access method is fully demonstrated,which provides a reference for the future application of WBAN in various scenarios.