| Wireless Body Area Networks(WBANs)are low-power and short-range wireless communication networks composed of a number of sensor nodes placed on the body surface or implanted in the body.The limited channel resources of WBAN and the variability of nodes in terms of transmission requirements,priority,etc.,pose more challenges to resource allocation.Channel resource allocation is the basis of communications in WBANs,and Medium Access Control(MAC)plays a vital role in channel resource allocation.However,the existing MAC protocols still have apparent shortcomings in node priority classification and channel resource allocation.On the one hand,the use of a fixed threshold to divide the node priority makes the quantification of the collected data not precise enough to distinguish the urgency degree difference of the nodes with the same priority;on the other hand,the fixed-length node access phase cannot adapt to the rapid change in resource demand of emergency nodes,thus resulting in insufficient or wasteful resource allocation.In order to improve channel resource utilization and reasonably design node priority,this paper proposes two MAC protocols for WBANs for low-traffic and high-traffic scenarios,respectively.The main contents are as follows:1)An adaptively adjusted MAC protocol based on priority(AA-MAC)protocol is proposed for low-traffic WBANs.In this protocol,an adaptive node priority is generated by a fuzzy inference system which considers multiple factors: vital signs,data rate,timeout rate and node location.The fuzzy inference method can remove the linguistic ambiguity of the above factors.Each superframe is dynamic and consists of a single non-contention phase and multiple differentiated contention phases for high-priority nodes and other nodes,respectively.This helps ensure reliable transmission for high-priority nodes and achieve fair access for other nodes.The length of each phase of the dynamic superframe is allocated according to the number of nodes and the traffic load,to improve the channel resource utilization.Extensive simulations prove that the proposed protocol is better than other ones in terms of packet loss rate,throughput and fairness.2)An adaptive sensing MAC protocol based on priority and traffic(PTAS-MAC)protocol is presented for high-traffic WBANs.In the contention part of this protocol,a node prioritybased CSMA/CA scheme first assigns an initial fixed backoff value for the node and then assigns a staggered backoff window corresponding to the node priority if a conflict occurs,to reduce the contention conflicts.Furthermore,an adaptive partitioning scheme based on the channel state,which divides the contention phase by the channel state detected by the ordinary node,to ensure the reliability of the emergency node and improving the channel utilization.In the non-contention part of this protocol,first,a utility function is designed based on the traffic,the reliability and the priority of nodes.The number of time slots is allocated by maximizing the utility function,to ensure the efficient utilization of time slots.Second,based on change of data stacking status,the node determines the new or old type of data to be transmitted to improve data timeliness.Finally,the node transmission order is assigned according to the node priority and data lifetime.The high-priority and imminent timeout data are transmitted first to reduce latency.Extensive simulations prove that the proposed protocol is better than other ones in terms of data delay,throughput and packet loss rate. |
