Research On Reliable Medium Access Control Protocol For Wireless Body Area Networks

Wireless body area networks(WBANs)play an important role in medical and health system,and they are usually composed of several sensors and a coordinator.Because of the limited sensor energy and rigorous service requirements in WBAN,it’s vital to improve the reliability of data transmission.However,due to factors such as body shape obstruction and tissue absorption,the signal of sensors suffers from various fading,which can reduce the reliability of data transmission.Medium access control(MAC)protocol,as a component of communication protocol,plays a key role in network performance,such as reliability,energy consumption and so on.However,the existing MAC protocols have some shortcomings in choosing the transmission method and occasion.On the one hand,dynamic sleep method allows sensors to go to sleep directly when channel quality is poor,which makes nodes unable to send data for a long time,resulting in data loss.On the other hand,the blind allocation of time resources cannot guarantee that the sensors have good channel conditions during transmission,resulting in lower reliability and higher energy consumption.In view of the shortcomings of existing research,this paper divides the networks into dynamic unstable and dynamic stable WBANs according to the stable state of human motion mode,and then designs MAC protocols based on various network characteristics.The main contents are as follows:Firstly,a medium access control based on sensor-disconnected duration(SDMAC)is proposed for dynamic unstable WBANs.The protocol allows sensor adaptively adjust the data transmission method according to the disconnection duration with the coordinator.For shortterm disconnection,emergency sensors detect channel quality in advance,and then flexibly swap time slot with ordinary sensors when channel quality is good to transmit data,which can reduce the waste of energy due to blind transmission,and increase data transmission opportunities and improve transmission reliability.For long-term disconnection,sensors choose a two-hop link with high transmission success rate and sufficient energy to transmit data.Compared with the existing fixed-link protocols,the adaptive transmission method of SDMAC protocol based on the disconnected duration improves the transmission reliability of long-term disconnected sensors,and saves the overhead of short-term disconnected sensors.Simulation and comparison experiments show the advantages of the proposed protocol in transmission success rate,throughput and energy consumption.Secondly,a medium access control based on channel state shift features(CSSF MAC)is proposed for dynamic stable WBANs.Firstly,the protocol determines the sensor slot allocation scheme according to the basic transmission slot demand of the sensors,the total number of transmission time slots provided by the network,the degree of sensor hunger and sensor priority.Specially,the degree of sensor hunger is depended on the proportion of the successfully transmitted data of sensor and the time interval between sensor’s successful communication,which can more reasonably measure the urgency of communication between the sensors and the coordinator.Secondly,the protocol allocates slot area and designs weight factor according to the features of markov channel model,and then decide the sensor transmission order based on the slot area and the weight factor.This approach improves the success probability of emergency data transmission,and reduces the conflict of slot allocation,so as to improve the reliability of data transmission.Simulation and comparison experiments show that the proposed protocol is effective in frame loss rate,throughput and energy consumption.