Research On Organization Planning And Multi Rate Transmission Technology In Underwater Acoustic Sensor Networks

As a new network form and monitoring means, Underwater Acoustic Sensor Networks (UWASNs) has become a recent research focus, which has wide application prospect in fields such as environment monitoring and protection, resources exploration, supplemental navigated water economy, disaster rescue and military defense; also has far-reaching influence on the safeguard of national defense and oceanic economy. However, in underwater acoustic channel, the limited frequency bandwidth, strong multiple path interference, random channel changes in time and space domain and high background noise in ocean environment together turn high speed and robust underwater acoustic communication into a recognized challenge. The propagation speed of underwater acoustic signal is five orders of magnitude lower than that of terrain radio signal and underwater acoustic signal attenuates quickly, so how to reduce network delay and node energy consumption is one of the key techniques in UWASNs. Aiming to reduce network delay, improve network energy utilization and prolong network lifespan, this paper mainly studies the technology of multi rate transmission and organization planning in underwater acoustic network.This paper first investigates the underwater channel in UWASNs, analyzes current multi rate access techniques and the application of OFDM based acoustic communication, and then derives the relation model between distance and optimal carrier frequency as well as bandwidth in underwater acoustic channel. By adaptive method of channel detection, multi rate transmission mechanism basing on OFDM and channel detection is obtained. This approach takes into account the frequency selectivity and practical characteristics of acoustic channel, and uses the signal noise ratio of each sub-band with different modulation schemes so that channel transmission rate is greatly improved, network delay is decreased and network throughput and transmission efficiency are enhanced as a whole.In addition to multi rate transmission, this paper further studies the self-organization and network planning in UWASNs, which focuses on the layout of surface gateways, underwater node route generation, clustering algorithm and slot allocation. Considering characteristics in underwater sensor networks, combining surface gateways number and position with sensor network nodes layout, network routes and gateway layout are derived according to different optimization goals, which decreases network delay, energy consumption and packet loss ratio. Through the relation between the position and load of cluster head as well as the spatial relationship among nodes, a clustering algorithm based on GA-WCA is proposed, which realizes cluster head localization using GA and in-cluster nodes selection using WCA. Compared to traditional WCA mechanism, GA-WCA mechanism has lower network delay and more balanced load of cluster head, and thus prolong network lifespan. Grounded on the fact that a slot can be shared by several nodes free of conflict, a simultaneous transmission approach for routing selection is presented, in order to reduce the whole network transmission delay and enhance network throughput.