Performance Analysis And Improvement Of NP-CSMA Protocol For Underwater Acoustic Networks

With the shortage of land resources and the development of technology,people begin to pay close attention the vast ocean.Underwater acoustic networks(UANs)is considered as an important way to explore the ocean resources and has received a lot of attention.Currently,most of the ocean-related applications are based on the UANs,such as pollution monitoring,disaster warning,mine reconnaissance,offshore exploration,etc.Typical underwater acoustic channels have the features of low bandwidth,long propagation delay,severe multipath and Doppler effect.The Medium Access Control(MAC)protocol plays an importance role on determining the multi-node accessing the shared channel,reducing the propagation delay,formulating the packet transmitting mechanism,maintaining the fairness of the network.Therefore,a high-performance MAC protocol is very demanding to improve the UANs throughput.CSMA is a class of wide applications MAC protocol,and its modeling analysis and performance research have become more mature on terrestrial network.However,there is little modeling analysis for CSMA in UANs.The evaluation of the MAC protocol for UANs has the following differences from that of terrestrial:since the land with light or electromagnetic waves as the information carrier,the propagation delay is negligible.it arises collision only when two or multiple nodes transmit packet simultaneously;On the other hand,sice the UANs use the acoustic wave with slow speed as the carrier of information,the long propagation delay cannot be ignored and a plurality of nodes transmitting data packets may not produce collision.Only when the two different data packets or more packets arrive receiving node at the same time or other data packets arrive the receiving node in the receiving packet period,these cases are thought as generating collision.In this paper,we first obtain the normalized throughput of NP-CSMA(Non-Persisent CSMA)protocol in the multiple-transmit multiple-receive scenario of UANs.The simulation results show that the throughput of NP-CSMA protocol in UANs is higher than that in the terrestrial network.Then,this paper studies the impact of the contention window on the NP-CSMA protocol,and analyzes the drawbacks of the NP-CSNA protocol in the underwater acoustic network.Aiming at these two points,this paper proposes a MAC protocol for UANs,which is referred to as the D-CSMA(Distributed contention window CSMA)protocol.Finally,the existing protocols and D-CSMA protocol are simulated on the NS-3 platform in terms of the measure metrics of different network sizes,different traffic volumes,the normalized throughput,successful transmission probability,average end-to-end delay and average energy consumption.Simulation results show that the proposed D-CSMA protocol achieves higher normalized throughput and successful transmission probability,lower end-to-end delay and average power consumption.