TDMA-based MAC Protocol For Small-scale Underwater Acoustic Sensor Networks With Mobile Access

Under-Water Acoustic Sensor Networks(UW-ASNs)feature long propagation delay,high bit error rate,multipath,Doppler effect and narrow available bandwidth,which is the reason why terrestrial proven MAC protocols can't be applied.MAC protocol is mainly responsible for allocating shared channel resource,thus reducing data transmission collision among nodes,which is vital for network communication.Taking the features of UW-ASNs for MAC protocol design into account,this paper designs two effective MAC protocols which ensure timely and collsion-free mobile access for the occasion where one or two mobile nodes exist in a fixed small-scale network.We propose a Location-based TDMA MAC Protocol for underwater acoustic networks with Mobile nodes(LTM-MAC)when mobile nodes want to communicate with the fixed nodes in a single-hop network.When a mobile node has data to send,the protocol will give it the highest priority to guarantee timely access.If mobile nodes have no data for some time,fixed nodes in the network will send one by one following the order making the idle waiting time shortest.Simulation and experiments show that LTM-MAC wins an advantage in terms of throughput,energy efficiency,access delay for mobile nodes in particular.We propose a TDMA MAC Protocol for Multi-hop underwater acoustic networks with Mobile Nodes(TMM-MAC)when mobile nodes want to communicate with the fixed nodes in a multi-hop network.We design the mechanism for mobile access on the basis of effective slot assignment algorithm and allow concurrent transmission if no collision occurs due to multi hop.In addition,considering long propagation latency,the protocol adopts two different strategies according to the length of the data packet to improve channel utilization.Simulation and experiments show that TMM-MAC satisfies the requirement that the mobile node can send as soon as possible without interference.