Design On MAC Protocol In Underwater Acoustic Self-Organized Network Based On NS2

Underwater acoustical sensor network, surveillance system as well as prewarning webturn out to be more and more urgent. The developing of underwater communicationtechnology has become an impending task.However, the special characteristics of underwater communication channel bring lots ofdifficulties in our researching. Comparing with terrestrial wireless sensor network, underwateracoustical sensor network has characteristics of strong multipath interference, narrowavailable frequency band, high environment noise, large attenuation and low transmissionspeed etc. which slow down the development of underwater acoustical self-organized network.Especially low transmission speed of underwater acoustical communication, which makeMAC(Medium Access Control) protocol of terrestrial wireless network can not apply inunderwater self-organized network directly.In this paper, we discuss the characteristics of underwater physical layer and embeddedunderwater propagation model, channel model and physical model in NS2, which is mostpopular network simulation tool. We compare the performance of ALOHA, CSMA(CarrierSense Multiple Access) and802.11protocols in underwater model such as throughput, packetaverage end to end delay, packets delivery rate. The simulation result shows that themechanism in802.11such as handshake and NAV(Network Allocate Vector) can also acquiremore packets in underwater environment. Although the other two performances are not verygood when using802.11as MAC protocol in simulation, we can amend parts of mechanismin802.11to meet the underwater environment, which can cut down the waste of time andadapt the underwater acoustic communications.This paper amends NAV mechanism based on standard802.11. The paper modify theframe structure of RTS/CTS/DATA/ACK to add timestamp field, which can calculate the realpropagation delay between two nodes, then setting neighbor NAV table dynamically to avoidthe waste of time. Simulation through NS2software with underwater model shows thatmodified DNMAC(Dynamic NAV MAC) protocol can adapt underwater environment betterthan standard802.11protocol. From the result we can see that the performance of throughputsand packets average end to end delay is improved accordingly.