| Underwater Acoustic Local Area Networks (UA-LANs) refer to the local area networks comprised of a number of underwater devices and a wireless Access Point (AP) which is used to provide wireless connections for the underwater devices through acoustic channel. UA-LANs can be widely used in ocean environmental monitoring, marine resources exploration and development, disaster early warning, military defense and the constructions of undersea laboratories and underwater emergency observation networks. Media Access Control (MAC), network access management and roaming handover of mobile nodes are fundamental issues for UA-LANs. They are key network technologies to ensure high efficient communication of UA-LANs and have great impact on the performance of UA-LANs. However, these key issues have not been solved effectively because of the application uniqueness of UA-LANs and the acoustic channel features of low-bandwidth, multi-path effects, random changes in high latency, high noise background and the Doppler Effect. In order to establish UA-LANs, in this paper, we study the MAC protocol, network access mechanism and underwater handover method for UA-LANs.First of all, aiming at the low channel utilization problem caused by acoustic channel features of limited bandwidth and high propagation delay, we study the efficient MAC protocol for single hop UA-LANs and propose a handshake based ordered scheduling MAC protocol. By combining the handshaking based channel reservation and the ordered scheduling data transmission mechanism, this protocol can achieve high channel utilization and can relax the requirement of time synchronization, meanwhile, it can adapt to the networks with mobile nodes.Based on the study of single hop UA-LANs, we futher focus on the multihop UA-LANs. For multihop UA-LANs, the transmission performance would be severely limited by unreasonable bandwidth allocation. Aiming at this problem, we first present a system model to optimize bandwidth for miltihop UA-LANs. Both the complicated interference relations between links and the different transmission demands of nodes are modeled. Thus, it can accurately reflect the characteristics of miltihop UA-LANs. According to the analysis results of a linear multihop network, a distributed traffic-based scheduling MAC protocol is proposed for multihop UA-LANs. By the joint optimization of bandwidth and channel utilization, this protocol can improve the performance of network effectively.Then, the network access problem of UA-LANs is studied, and a network access mechanism called lifetime and energy efficiency based multihop access protocol is presented. By dividing the network access procedure into three phases of network discovery, relay path determining, and association, this protocol can realize multihop network access function. Moreover, a path lifetime and energy efficiency based relay path selection algorithm which can prolong the network lifetime is developed in relay path determining phase.For the UA-LANs with mobile nodes, the mobility of nodes would lead the accessed nodes to roam to another network. Thus, we further study the roaming handover technology for UA-LANs. Firstly, the change of Receive Signal Strength (RSS) of underwater nodes is analyzed. Then, according to the analysis results, a handover protocol based on RSS trend and historical access information is proposed for UA-LANs, and the adaptive seamless roaming handover can be realized.At last, based on the above theoretical researches, we design and develop a prototype system of UA-LANs, then a series experiments are carried out to test and verify the system. The experiments results have confirmed the feasibility and effectiveness of the proposed MAC protocol, network access mechanism and underwater handover protocol. |
PDF Full Text Request