Research On Hybrid MAC Protocol For Underwater Wireless Sensor Networks

In recent years,underwater wireless sensor networks(UWSNs)have attracted increasing interest due to their various underwater applications.Unlike terrestrial networks,underwater acoustic channels are characterized by low available bandwidth,long propagation delay and limited energy.Most of the existing MAC protocols focus on avoiding conflicts,while the issue of bandwidth allocation is not fully considered,which is easy to cause unfair competition on links and waste of channel resources.Therefore,it is particularly important to ensure the fairness of MAC protocols.In addition,underwater sensor nodes are powered by disposable batteries,so MAC protocols must pay attention to energy consumption performance.To sum up,aiming at the unfairness of channel sharing,this paper proposes a MAC protocol based on fair bandwidth allocation.Then,on this basis,a hybrid MAC protocol based on energy optimization is proposed to reduce energy consumption.The specific research work consists of the following two aspects.(1)To achieve fair channel sharing among multiple nodes,a MAC protocol based on fair bandwidth allocation(FBA-MAC)is proposed.The protocol sets an upper limit on the number of packets that can be transmitted in a data communication round to avoid the host node being in the receiving state for a long time due to excessive traffic at one node.In the scheduling period,the protocol first designs a bandwidth allocation mechanism in which the host node allocates available bandwidth to each node according to the transmission requirements of member nodes and the generation time of data packets.Then,the host node schedules the nodes to send packets based on the bandwidth allocation results for the purpose of effectively avoiding data collisions and reducing the waste of channel resources.Finally,the performance of FBA-MAC protocol and several existing MAC protocols is compared by simulation experiments.The results show that FBA-MAC protocol can obtain high fairness,and performs well in terms of throughput,end-to-end delay,energy consumption and packet delivery ratio under high network load,achieving the expected goals.(2)To achieve low energy consumption and ensure high fairness under different network loads,a hybrid MAC protocol based on energy optimization(HEO-MAC)is proposed.In response to the slightly higher energy consumption of FBA-MAC protocol when the traffic load is low,HEO-MAC protocol converges ALOHA protocol,which has good performance at low load,and FBA-MAC protocol to give full play to the advantages of the two sub-protocols.The hybrid protocol provides a method for determining the load switching threshold,and then uses the load switching threshold to judge the level of traffic load,so as to dynamically switch the two sub-protocols.ALOHA protocol is selected when the network load is low and FBA-MAC protocol is used when the monitoring node finds that the network traffic is greater than the load switching threshold.Finally,the simulation experiments verify that HEO-MAC protocol combines the advantages of both sub-protocols and performs well in terms of energy consumption and fairness,while providing good throughput,end-to-end delay and packet delivery ratio performance.